Eleven Vietnamese sailors were missing in the East Sea after their cargo ship sank during high winds, rescue officials said Wednesday (December 29), warning other mariners to steer clear of bad weather.

Twelve seamen were rescued by fishermen after the Van Don-2 sank early Tuesday about 400 kilometers (250 miles) off the coast of Ba Ria-Vung Tau, said Bui Ngoc Tri, of the southern province’s search and rescue center.

"We have sent two rescue boats and asked fishing vessels in the area to help in the search for missing sailors," Tri said.

"However, our search is hampered by bad weather."

Tri said the accident happened very quickly during heavy seas, and he did not know whether the crew had time to put on their life jackets.

"We are making maximum efforts to search for them and I can’t talk about their chances of survival. That depends a lot on the energy of each one of them, and on the weather conditions."

Another rescue official, Vu Khac Cuong, said on state television that the 12 survivors were all in a poor condition, and two were injured.

The ship, weighing 6,900 deadweight tons, was transporting material for iron manufacturing from Malaysia to Ho Chi Minh City, Tri said. It belongs to the Quang Ninh Sea Transport company based in the northern Quang Ninh Province.

A staffer at the shipping company said they were waiting for more information from the rescue center.

Strong winds and heavy seas are common off Vietnam’s coast at this time of the year, and Cuong said the latest incident shows that shippers should take heed.

"It’s a warning to the owners of cargo ships about maritime safety, and unexpected changes in the weather at sea," he said.

Twenty other fishermen were missing and presumed dead after their vessel overturned on December 17, by strong winds off Ba Ria-Vung Tau Province. Only one man survived, a rescue official said.

Local media reported that another 23 seamen have not been found after the Phu Tan container ship from Vietnam sank on December 16 during severe weather further north, to the west of China’s Hainan island.

Officials said rescue workers from China and Vietnam found three survivors and one body from the cargo ship.