Thai rescuers were hunting on Wednesday for an army helicopter with nine people aboard that went missing during a mission to retrieve five bodies from a previous crash, a military spokesman said.
The Black Hawk chopper disappeared on Tuesday in an area of dense jungle on the Thai-Myanmar border after it was dispatched to recover the bodies of soldiers killed in a helicopter accident on Saturday.
"So far there is no contact from the lost aircraft or passengers," army spokesman Colonel Sunsern Kaewkumnerd told AFP.
"The search operation began at 6:30am (2300 GMT Tuesday) with several teams, each comprising seven soldiers, who have spread out on foot to search the area," he added.
Soldiers in neighbouring Myanmar reported hearing a loud noise near the area, but were unable to locate a crash scene, according to Siriyon Phothibandit, a Thai official at the Kaeng Krachan national park near the border.
"If it crashed we have high hopes some would have survived," he added.
Among the nine people on board the Black Hawk were Major General Tawan Ruengsri, commander of a border task force, and a television cameraman from army-run Channel 5.
In Saturday's crash, the aircraft went down in bad weather during a mission to airlift troops from the remote jungle area southwest of Bangkok.
The helicopter had been sent to collect about 35 soldiers who had been on patrol in the park as part of measures to combat deforestation, but crashed close to the pick-up site. Those soldiers are still there.