Five crew members were missing and five others were rescued after a Chinese fishing boat capsized off South Korea's southern coast on Wednesday, the South Korean coastguard said.

The boat keeled over while being towed by another Chinese fishing boat after developing engine problems, a spokeswoman of the Mokpo Coastguard said.

The accident occurred early Wednesday, some 85 kilometres (52 miles) northwest of Gageo Island in Shinan County. 

"Four crew members were immediately rescued by a nearby Chinese fishing boat, while another was plucked from the icy water by a South Korean patrol boat. But he remains unconscious".

"Five others are still missing", she said.

Seven boats from the South Korean coastguard and its navy, backed by four aircraft, are combing the area, she added.

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