Updated

Eleven crew members from a Bangladeshi cargo ship were missing Thursday after their vessel capsized in the Andaman Sea, sparking a rescue mission, Thai officials said.

The ship, which was heading for Bangladesh's port of Chittagong, ran into trouble early Thursday in rough seas some 32 kilometres (20 miles) off an island near Phuket in Thailand's south.

Six of the crew were rescued, five of them by a passing ship and the other by a navy helicopter, according to Phuket marine police.

But fears were growing for the 11 missing after several hours without a sighting.

"There were 17 crew in total," Major Chatchai Sakdee added, revising down early reports of 28 on board and 18 rescued after initial "confusion... from information from different sources".

Marine police Lieutenant Colonel Prasert Srikunrat said "very poor visibility" was hampering the search for the missing.

The Thai navy said the missing were in a lifeboat which was set adrift by the high seas.

"We cannot find them yet after two trips by helicopters, and one by an airplane... there's heavy rain and poor visibility," Thammawut Marlaisukarin, a captain in the Thai navy, told AFP, confirming the figures.

"The ship capsized in rough seas -- there are five-metre (16 feet) high waves in the Andaman Sea near Phuket now," he added.

Phuket is Thailand's biggest island and one of its most popular tourist destinations.