Rescue workers, police and even coal miners are combing the site where a Malaysian jet crashed after being shot from the sky by what US intelligence officials believe was a surface-to-air missile, scattering wreckage and bodies across the Ukrainian countryside.

For the second time in five months, a Malaysia Airlines plane filled with international passengers and crew was lost - an unthinkable coincidence.

The cause of yesterday's crash was not immediately clear. Ukraine accused pro-Russian separatists of shooting down the plane which was flying from Amsterdam to Kuala Lumpur with 298 people on board. The rebels denied it.

Off-duty coal miners joined the search effort early today in fields near the rebel-held village of Hrabove in the Donetsk region of eastern Ukraine, about 40km from the Russian border, where fighting has raged for months.

Large chunks of the Boeing 777 that bore the airline's red, white and blue markings lay strewn over a field.

The cockpit and one of the turbines lay more than 1km apart, and residents said the tail landed about 10km away, indicating that the aircraft probably broke up before hitting the ground.

An Associated Press journalist saw bodies and body parts strewn across the field outside the village of Rozsypne about 4km away from the crash site.

American intelligence authorities believe a surface-to-air missile brought the plane down but are still working on who fired the missile and whether it came from the Russian or Ukrainian side of the border, a US official said.

Malaysia's prime minister said there was no distress call before the plane went down and that the flight route was declared safe by the International Civil Aviation Organisation.

More than half of the passengers on board - 154 - were Dutch citizens, with 43 from Malaysia, including the 15 crew members. Another 27 were Australians, 12 from Indonesia, and nine Britons. The victims included three infants.

Ukrainian President Petro Poroshenko called it an "act of terrorism" and demanded an international investigation. He insisted his forces did not shoot down the plane.

Earlier this week, the rebels claimed responsibility for shooting down two Ukrainian military planes.

In Kuala Lumpur, several relatives of those on board the jet gathered at the international airport.

A distraught Akmar Mohamad Noor, 67, said her older sister was coming to visit the family for the first time in five years. "She called me just before she boarded the plane and said, 'See you soon,'" she said.

Counsellors were meeting with a few family members in the airport viewing gallery, sealed off from a horde of journalists. One woman emerged in tears and was escorted out of the airport by a security officer without saying anything.

"This is just too much," said Cindy Tan, who was waiting at the airport for a friend on another flight. "I don't know really why this happened to a MAS (Malaysia Airlines) plane again."

Ukraine's security services produced what they said were two intercepted telephone conversations that showed rebels were responsible. In the first call, the security services said, rebel commander Igor Bezler tells a Russian military intelligence officer that rebel forces shot down a plane. In the second, two rebel fighters - one of them at the crash scene - say the rocket attack was carried out by a unit of insurgents about 15 miles (25km) north of the site.

Neither recording could be independently verified.

Russia's Interfax news agency quoted Sergey Kavtaradze, a special representative of the Donetsk People's Republic leader, as denying that the intercepted phone conversations were genuine.

US President Barack Obama called the crash a "terrible tragedy" and spoke by phone with Russian President Vladimir Putin as well as Mr Poroshenko. Britain called for an emergency meeting of the UN Security Council on Ukraine.

Later, Mr Putin said Ukraine bore responsibility for the crash, but he did not address the question of who might have shot it down and did not accuse Ukraine of doing so.

"This tragedy would not have happened if there were peace on this land, if the military actions had not been renewed in southeast Ukraine," he said, according to a Kremlin statement issued early today. "And, certainly, the state over whose territory this occurred bears responsibility for this awful tragedy."

At the United Nations, Ukrainian Ambassador Yuriy Sergeyev told the AP that Russia gave the separatists a sophisticated missile system and thus Moscow bears responsibility, along with the rebels.

Australian Prime Minister Tony Abbott told Parliament today that authorities owe it to the families of the dead to find out exactly what happened and who was responsible.

"As things stand, this looks less like an accident than a crime. And if so, the perpetrators must be brought to justice," he said.

US Secretary of State John Kerry said he was "horrified" by the crash, and the United States was prepared to help with an international investigation.

Ukraine's crisis began after pro-Moscow President Viktor Yanukovych was driven from office in February by a protest movement among citizens angry about endemic corruption and seeking closer ties with the European Union.

Russia later annexed the Crimean Peninsula in southern Ukraine, and pro-Russians in the country's eastern regions began occupying government buildings and pressing for independence. Moscow denies Western charges that it is supporting the separatists or sowing unrest.

Kenneth Quinn, of the Flight Safety Foundation, said an international coalition of countries should lead the investigation. Safety experts say they are concerned that, because the plane crashed in area of Ukraine that is in dispute, political considerations could affect the investigation.

The RIA-Novosti agency quoted rebel leader Alexander Borodai as saying that talks were under way with Ukrainian authorities on calling a short truce for humanitarian reasons. He said international organisations would be allowed into the conflict-plagued region.

Aviation authorities in several countries, including the FAA in the United States, had issued warnings not to fly over parts of Ukraine prior to yesterday's crash, but many carriers, including cash-strapped Malaysia Airlines, had continued to use the route because "it is a shorter route, which means less fuel and therefore less money," said aviation expert Norman Shanks.

Within hours of the tragedy, several airlines said they were avoiding parts of Ukrainian airspace.

A US official said American intelligence authorities believe the plane was brought down by a surface-to-air missile but are still working to determine additional details about the crash, including who fired the missile and whether it came from the Russian or Ukraine side of the border.

But American intelligence assessments suggest it is more likely pro-Russian separatists or the Russians rather than Ukrainian government forces shot down the plane, according to the official.

The United States has sophisticated technologies which can detect missile launches, including the identification of heat from the rocket engine.

Anton Gerashenko, an adviser to Ukraine's interior minister, said on his Facebook page the plane was flying at about 10,000m when it was hit by a missile from a Buk launcher, which can fire up to an altitude of 22,000m. He said only that his information was based on "intelligence".

Igor Sutyagin, a research fellow in Russian studies at the Royal United Services Institute, said both Ukrainian and Russian forces have SA-17 missile systems - also known as Buk ground-to-air launcher systems.

Rebels had recently bragged about having acquired Buk systems.

Mr Sutyagin said Russia had supplied separatists with military hardware but had seen no evidence "of the transfer of that type of system from Russia".

Earlier yesterday, AP journalists saw a launcher that looked like a Buk missile system near the eastern town of Snizhne, which is held by the rebels.

Mr Poroshenko said his country's armed forces did not shoot at any airborne targets.

Separatist leader Andrei Purgin told the AP he was certain that Ukrainian troops had shot the plane down, but gave no explanation or proof.

There have been several disputes over planes being shot down over eastern Ukraine in recent days.

A Ukrainian fighter jet was shot down on Wednesday by an air-to-air missile from a Russian plane, Ukrainian authorities said, adding to what Kiev says is mounting evidence that Moscow is directly supporting the insurgents.

Pro-Russia rebels claimed responsibility for strikes on two Ukrainian Sukhoi-25 jets on Wednesday. Ukraine's Defence Ministry said the second jet was hit by a portable surface-to-air missile but the pilot landed safely.