Authorities dispatched planes and helicopters to aid in the rescue, with at least three people from the crew of 30 brought to safety as of 5:30 p.m. local time (5:30 a.m. ET) Saturday.
Photos released by the Hong Kong Government Flying Service showed one crew member being winched up to a rescue helicopter as big waves lashed the sinking vessel, which had broken up in two parts.
The accident occurred about 186 miles south of Hong Kong.
The Flying Service did not give the name or origin of the vessel. It said in a statement that crew members were negotiating difficulties brought on by Severe Tropical Storm Chaba, which was packing maximum winds of 68 miles per hour.
The storm made landfall in the western part of the coastal province of Guangdong later Saturday.
The Hong Kong service sent two fixed-wing aircraft and four helicopters for the rescue effort.