Three British tourists, including a child, were killed and four others were seriously injured after their vehicle plunged off a high bridge in Iceland on Thursday, police said.

Two children were among the four injured when the vehicle carrying the seven people crashed around 9:30 a.m. Thursday, Icelandic police said. The vehicle was traveling on road No. 1, an 830-mile road that stretches to a one-lane bridge at Skeidararsandur, a vast sand plain in southern Iceland, when it slammed through a railing.

"It was horrible," said tour guide Adolf Erlingsson, who was among the first to arrive at the crash scene.

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Erlingsson said the vehicle, a Toyota Land Cruiser according to the BBC, “flew” off the bridge, landing onto a rocky river bank.

"The car was totally smashed up after flying off the bridge and plunging down there,” he said. "When I arrived four had been retrieved from the vehicle, one was dead and three still stuck in the car, two of them probably dead. It was just awful.

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"The car seemed to have hit the ground many meters from where it stopped. We struggled [with] getting everyone out,” Erlingsson added.

It’s unclear what caused the crash or how the driver lost control of the vehicle. According to multiple reports, the tourists were in a 4x4. It wasn't clear which make or model.

Iceland has seen a boom in tourism in recent years, with 2.5 million visitors in 2018, according to the Icelandic Tourist Board. Infrastructure, however, has struggled to keep up with the growing number of tourists. At least 18 people, half of them foreigners, have died in traffic accidents this year.

The Associated Press contributed to this report.