"We are preparing means to be ready to carry out search and rescue," said Luu Duc Tung, deputy head of Vietnam Maritime Rescue Coordination Centre.
The Russian-built Su30-MK2 jet fighter, carrying two pilots, lost contact at 8:15 am (0115 GMT) over Nghe An province, Thanh Nien newspaper reported.
Fisherman Le Van Cuong informed the rescue force at 8:30 am that he saw a plane crash near Mat island around 20 kilometres off Nghe An.
Phan Xuan Hai, a coast guard official, said his unit has sent three ships with 35 people to search for the plane, but has not found it yet, Thanh Nien said.
The long-range strike fighter Su30-MK2 was developed by the Sukhoi Company.
- DPA