Authorities in the central province of Quang Ngai said Friday they had saved 103 fishermen on 16 vessels that sank Thursday off its coast due to rough seas.
According to the provincial departments of flood prevention and rescue, the vessels were damaged after a tornado slammed into the waters off Quang Ngai coast.
The same day, a cargo ship capsized in waters off the central province of Ha Tinh leaving 25 sailors and two passengers missing in strong gales and rough seas.
The victims have not been heard from since while harsh conditions are preventing rescue ships from reaching the site where the Phu Tan went down, about 120km off the coast of Ha Tinh Province.
Hai Phong Port Authorities received a distress call from the ship at around 7.30am reporting that the ship was sinking and a few hours later, they lost contact with the ship.
The Hai Phong Port Authority said the sailors and passengers may have fallen overboard.
The Maritime Search and Co-ordination Center for Region 1 dispatched rescue vessels to search for the ship and ordered the Song Cau oil tanker which was operating near the scene to help with the rescue mission.
According to Xinhua News Agency, Chinese maritime rescue authorities also dispatched a rescue vessel to help after receiving emergency calls from their Vietnamese counterparts.
The Phu Tan was owned by the Vietnam National Shipping Lines Company and had a loading capacity of 140,000 tons. It was on its way to Hai Phong from Ho Chi Minh City when the accident happened.
Thursday's extreme weather conditions also damaged eight fishing boats with a total of 53 men on board, said Phan Van On, head of the Committee for Flood and Storm Control in the fishing province of Quang Ngai.
Two sank, two were rescued and the remainder took on large amounts of water after springing leaks.
Local authorities have instructed rescue teams to conduct search and rescue work.