Officials say a Jeep carrying seven British tourists has crashed while crossing a high bridge in Iceland, killing three and critically injuring four others.

Icelandic police said one child was among the dead, and two other children were severely hurt.

The accident occurred around 9.30am on Thursday local time when the vehicle slammed through a railing on a one-lane bridge at Skeidararsandur, a vast sand plain on the southern shore of Iceland.

The car landed about nine metres below on a rocky river bank.

Police say it remains unclear what caused the British driver to lose control of the vehicle but temperatures were around freezing at the time.

The accident occurred hours before the North Atlantic island saw sunrise, which hit the capital, Reykjavik, at 11:23 a.m. on Thursday.

Tour guide Adolf Erlingsson was among the first on the scene. “It was horrible,” he told The Associated Press. “The car seemed to have hit the ground many meters from where it stopped. We struggled getting everyone out.”

Police only identified the victims as British; their names and ages have not been released.

The four who survived were flown by helicopter to a hospital in Reykjavik.

The accident took place on Road No. 1, which runs for 1,337 kilometres as it connects coastal towns and villages on this volcanic island of 350,000 people.

Iceland has seen a gigantic tourist boom in the last several years but its infrastructure has not always kept up.

Roads are usually narrow, with many one-lane bridges.

The bridge over Núpsvötn was built in 1973 and is the second-longest bridge in the country, according to Icelandic news website Visir.

The bridge is said to have been the scene of a number of accidents in recent years and is reportedly expected to be replaced soon with a shorter bridge around a quarter of the length.

Of the 18 people who have died in traffic accidents in Iceland this year, half of them have been foreign nationals.

Last year was the first on record when more foreigners died than residents, according to the Icelandic Transport Authority.

This year 2.5 million tourists visited Iceland, drawn to its volcanic landscapes and northern lights, compared with half a million in 2011, according to the Icelandic Tourist Board.