HANGZHOU: Rescuers were last night searching for 17 workers missing in the cave-in of a subway tunnel on Saturday which killed four people.

"There is a very slim chance of their survival as the crater is flooded with water," Hangzhou government deputy secretary-general Wang Guangrong told a press conference in the morning.

The accident is one of the worst in the history of subway construction in the country; and six people are being treated in hospital, he said.