Iranian emergency services were bracing for widespread flooding on Tuesday with mass evacuations planned as extensive rainfalls in regions neighbouring Khuzestan converge on the oil-rich southwestern province.

"The water moving south from Ilam and Lorestan provinces will enter Khuzestan... many villages there will be submerged," said Ali Asghar Peivandi, the head of Iran's Red Crescent.

"With the possibility of dams overflowing, we have made preparations to accommodate 100,000 people," he told state television.

Khuzestan has an extensive range of dams but officials said water was flowing into them at a fast rate.

In some cases water levels were only 70 centimetres lower than the dam crests, they reported.

"Our dams are more than 95 per cent full," Khuzestan governor Gholamreza Shariati told state TV.

Water was released from dams as an emergency measure to prevent them from breaking, leading to fears the outflow may cause havoc in cities, towns and villages downstream.

Iran has been hit by flooding across most of the country for the past two weeks.

The northeast of Iran was swamped on March 19 before the west and southwest of the country were inundated on March 25, killing a total 45 people.

This week the deluge hit the west and southwest, with at least four deaths already reported even though emergency services have only begun reaching regions cut off by floods.

"Seventy-eight intercity roads have been blocked, as many as 2,199 rural roads and 84 bridges have been washed away," said Behnam Saeedi, spokesman for the National Disaster Management Organisation.

"Across 15 provinces, 141 rivers burst their banks and around 400 land slides were reported," he told state TV.

The main rail links between Tehran and the south and north of the country was disrupted as landslides and water swept away tracks.

The government said the flooding had damaged nearly 12,000 kilometres of roads, or 36 per cent of the country's entire network.

Rescue efforts overnight were hindered by the inability of Iran's ageing and limited rescue helicopter fleet to fly at night.

US sanctions stop Iran from purchasing helicopters, prompting Foreign Minister Javad Zarif to accuse the United States of impeding aid efforts.

The sanctions were "impeding aid efforts by #IranianRedcrescent to all communities devastated by unprecedented floods," Zarif tweeted.

"Blocked equipment includes relief choppers, this isn't just economic warfare; it's economic TERRORISM," he wrote.

The military has been called in to help the emergency services cope.

Drones surveyed flooded regions looking for survivors as choppers and amphibious armoured personnel carriers were used to evacuate stricken residents.