Egypt has unveiled a major extension of the Suez Canal billed by President Abdel-Fattah el-Sissi as a historic achievement needed to boost the country's ailing economy after years of unrest.

Mr El-Sissi, wearing his ceremonious military uniform and trademark dark sunglasses, flew to the site aboard a military helicopter and immediately boarded a monarchy-era yacht that sailed to the venue of the ceremony.

The yacht was flanked by navy warships as helicopters, jet-fighters and military transport aircraft flew overhead.

A visibly triumphant Mr el-Sissi stood on the vessel's upper deck, waving to well-wishers and folklore dance troupes performing on shore.

At one point, a young boy in military uniform and holding an Egyptian red, black and white flag joined him on deck.

Later in the day, the president changed to a dark grey business suit and took his seat at the main stand for an elaborate ceremony in the canal city of Ismailia, attended by foreign dignitaries and organised amid tight security measures following a series of attacks by Islamic militants in the Sinai Peninsula and the capital, Cairo.

Among those at the ceremony were French president Francois Hollande, King Abdullah of Jordan and Bahrain's King Hamad bin Isa Al Khalifa. Palestinian president Mahmoud Abbas, Kuwait's emir Sheik Sabah Al Ahmed Al Sabah and Greek prime minister Alexis Tsipras also attended.

The unveiling of the $8.5 billion extension has been trumpeted as a historic achievement by pro-government media and has revived the nationalistic personality cult built around the 60-year-old Mr el-Sissi, who as army chief led the overthrow of an Islamist president in 2013 and was elected to office last year.

Egypt's black, white and red flags now adorn streets across much of the nation, along with banners declaring support for Mr el-Sissi and hailing his latest achievement. The government declared Thursday a national holiday, and banks and most businesses were closed.

The new Suez Canal extension involved digging and dredging along 72 kilometres of the 193-kilometre canal, making a parallel waterway at its middle that will facilitate two-way traffic.

With a depth of 24 metres, the canal now allows the simultaneous passage of ships with up to 66 feet draught.

The project was initially estimated to take three years, but Mr el-Sissi ordered it be completed in one.

The government says the project, funded entirely by Egyptian investors, will more than double the canal's annual revenue to $13.2 billion by 2023, injecting much-needed foreign currency into an economy that has struggled to recover from the 2011 uprising that toppled president Hosni Mubarak and the years of turmoil that followed.

Economists and shippers have questioned the value of the project, saying the increased traffic and revenues the government is hoping for would require major growth in global trade, which at this point seems unlikely.

But the man-made waterway linking the Red Sea to the Mediterranean, which was inaugurated in 1869, has long been seen as a symbol of Egyptian national pride.

And pro-government media has compared Mr el-Sissi to former president Gamal Abdel Nasser, whose nationalisation of the canal in 1956 is seen as a defiant break with the country's colonial past.

"Egypt makes history," read the banner headline of Thursday's pro-government daily Al-Watan. The front page of another daily, Al-Maqal, said "Rejoice, it is worth it!"

But today's ceremony was partially overshadowed by an Islamic State (IS) affiliate's threat to kill a Croatian hostage kidnapped in Cairo last month - a grim reminder of the threat posed by Islamic militants to Egypt's stability.

The affiliate, calling itself the Sinai Province of the Islamic State, released a video on Wednesday threatening to kill the Croatian in 48 hours if Egyptian authorities do not release "Muslim women" held in prison, a reference to female Islamists detained in the government's broad crackdown on former president Mohammed Morsi's supporters.

The 30-year-old Croatian father of two, Tomislav Salopek, was kidnapped on July 22.

Croatian state TV reported on Thursday afternoon that foreign minister Vesna Pusic had left for Cairo together with Salopek's wife, Natasa.

Egypt has seen a surge in attacks by Islamic militants since Mr Morsi's ouster, in both the restive north of the Sinai Peninsula and the mainland, focusing primarily on security forces.

The violence continued today, with militants shelling two homes near security checkpoints in northern Sinai, killing two people and wounding nine, according to Egyptian security officials who spoke on condition of anonymity because they were not authorized to speak to the media.

A soldier standing guard at a military checkpoint in northern Sinai was also killed by sniper fire, the officials said.

Militants have also targeted foreign interests, including the Italian consulate in Cairo, which was hit with a car bomb last month. That came just days after another bomb killed Prosecutor General Hisham Barakat in an upscale Cairo neighbourhood.

However, Wednesday's video was the first to be released by Islamic militants showing a kidnapped foreigner in Egypt, an ominous escalation as the country tries to rebuild its vital tourism industry. The professionally-made video resembled clips released by the IS group in Syria and Iraq, indicating closer ties with its Egyptian branch.

Sign up to our free newsletters

Get the best updates straight to your inbox:
Please select at least one mailing list.

You can unsubscribe at any time by clicking the link in the footer of our emails. We use Mailchimp as our marketing platform. By subscribing, you acknowledge that your information will be transferred to Mailchimp for processing.