A search and rescue operation is underway to determine the fate of the plane.
Debris of a Myanmar military plane which went missing with 120 people on board was found in the Andaman Sealate on Wednesday, a local official said.
The Chinese-made Y8-200F transport plane lost contact 29 minutes after take off at the coastal town of Myeik to head Myanmar's largest city of Yangon, officials said.
"Now they have found pieces of the damaged plane in the sea 218 km away from Dawei city," said Naing Lin Zaw, a tourism official in Myeik, adding the navy was still searching the sea.
An air force source confirmed that a navy search and rescue ship had found pieces of the plane in the sea an hour's flight south of Yangon, Myanmar's commercial capital.
"We don't know what exactly happened to this plane after the loss of contact," said Kyaw Kyaw Htey, a civil aviation official at Myeik airport.
Kyew said weather had been "normal" with good visibility when the plane took off.
Civil aviation authorities initially said there were 105 people onboard. The military later said those on board included 106 soldiers and family members and 14 aircraft staff. The maximum capacity of the aircraft is 200 people, said a military officer.
The plane was bought in March 2016 and had a total of 809 flying hours. It was carrying 2.4 tonnes of supplies, the military said.
A former executive at the aviation ministry said many of the aircraft in Myanmar's fleet were old and decrepit.
"Myanmar air force has very bad safety performance," he said, asking to remain nameless.
Myanmar's military fleet has a chequered recent history of plane crashes.
All five crew died when an air force plane burst into flames soon after taking off from the capital Naypyidaw in February last year.
Three army officers were killed in June when their Mi-2 helicopter crashed into a hillside and burst into flames in south-central Bago.