Forty-seven Vietnamese sailors were missing, most of them from a cargo ship and a fishing vessel, and six others were confirmed dead after storms hit the South China Sea, officials said Tuesday.
A source at the national search and rescue centre said 20 fishermen were missing and presumed dead after their boat overturned last Friday.
"We don't think there are signs of survival. But we will keep trying to look for them," said the official, asking not to be named.
He quoted the only survivor of the accident as saying none of the sailors was able to put on a life jacket.
Another 23 missing seamen belonged to the Phu Tan container ship that capsized and sank Thursday about 185 kilometres (115 miles) west of Sanya city on China's Hainan island.
Officials said rescue workers from China and Vietnam found three survivors and one body from the cargo ship, which belonged to Vinalines Container Shipping Company.
"We are still trying to look for any signs of the victims. But bad weather and containers floating at the accident site have hampered our effort," the search and rescue official said.
The national flood and storm control department said four other sailors were also missing and five had died in separate incidents since bad weather and strong winds hit Vietnam's coast last Thursday.