HANOI, June 16 -- A Vietnamese coastguard plane, which was searching for a missing fighter jet and its pilot, disappeared off the radar on Thursday, state media and a military official said, the second such setback in three days.

The CASA C212 plane carrying nine people went missing off the northern province of Haiphong province about noon local time, local media reported, citing military and provincial sources.

The coastguard plane was joining thousands of people looking for a pilot who went missing with a Sukhoi SU-30 MK2 fighter jet on Tuesday along the central part of the country coastline.

A military official working on the rescue confirmed the plane was missing and the numbers on board but requested anonymity as he was not authorised to speak to the media.

He said the CASA plane was descending in order to approach objects the crew believed were the search targets.

A senior military official in charge of the search did not answer his phone when contacted by Reuters. A coast guard official in charge of media said he had no official information to confirm the news.

One of the two pilots flying the Sukhoi jet was rescued from the sea on Wednesday. Coastguards, border guards, navy, air force and fishermen have been searching for the aircraft and the second pilot for two and a half days.

Vietnam has suffered a series of mishaps in the past two years with ageing helicopters.

The country is recalibrating its defence strategy and overseeing its biggest military buildup in four decades, including buying more fighter jets and enlisting Japanese and U.S. help to strengthen Vietnam's coastguard through training, loans and aid for vessels.