A flash flood killed six German tourists and their two Thai guides late Saturday while exploring a cave at a national park in southern Thailand, police said.

A heavy rainfall sent water surging through the 500-metre-deep cave in Khao Sok national park in Surathani province, said police Lt.-Col. Pichan Kanayasiri.

"The tourists were inside the cave and didn't know what was happening outside," he said. "They were trapped inside the cave."

Rescue teams worked through the night trying to save the group.

Among the German victims were three women, two men and a 10-year-old boy. A British woman who was part of the tour group survived.

A Belgian tourist was killed by a flash flood in the same cave several years ago, Pichan said.

The province's governor, Winai Phopradit, said he had ordered the national park closed during the rainy season.

"We have signs both in English and Thai warning tourists not to go into the cave during heavy rains," he said.

With files from the Associated Press