GUANGZHOU, July 21 -- Rain-triggered floods have swollen rivers in south China's Guangdong Province and threatened marine safety, local authorities warned Tuesday.

Under the impact of a tropical depression and a monsoon, most parts of the province were hit by downpours in the past five days. The average precipitation topped 100 mm in many cities, whereas in the worst-hit counties, precipitation topped 300 mm, the provincial hydrological department said in a press release.

The downpour relieved a persisting drought on the Leizhou Peninsula, but raised several rivers to alarming levels as well, it said.

The weather bureau has forecast continuous rain in the eastern parts of the province and the Pearl River Delta Wednesday and Thursday, warning of flood, mountain torrents and subsequent geological disasters.

The stormy weather poses a threat to water traffic safety off the coast of Guangdong.

Four vessels capsized or sank off the coast of Guangdong Province Monday night, involving 36 sailors, the provincial maritime salvage center said in a press release Tuesday.

Rescuers from Guangdong and Hong Kong worked together in the search and rescue operations, which involved dozens of rescue boats and helicopters, it said.

As of 9 p.m., all the sailors had been saved.