The bodies of three foreign workers who were trapped for days in a railway tunnel in northeastern Thailand that collapsed during construction have been retrieved after an intensive rescue effort, Thai officials said Friday

The tunnel is a part of a Thai-Chinese high-speed railway project linking the capital Bangkok to the northeastern province of Nong Khai, bordering Laos.

Part of it collapsed on Saturday night while three foreign workers, one from Myanmar and two from China, were inside. The tunnel is in Nakhon Ratchasima province, 250 kilometers (155 miles) northeast of Bangkok.

Investigation of the accident is ongoing, but Thai media reported that Deputy Transport Minister Surapong Piyachote said Monday that it appeared that the earth above the tunnel had become especially heavy due to days of rain.

The body of one worker, a truck driver from Myanmar, was found Thursday and the other two on Friday, Interior Minister Anutin Charnvirakul told the media.

He said the two Chinese victims were a supervisor and a backhoe operator.

Autopsies carried out at a provincial hospital would ascertain the cause of death, he said.

“The initial result indicated that the first victim we found yesterday died of suffocation,” Anutin said.

The 126-hour rescue operation was led by the State Railway of Thailand and a rescue team from China, which arrived at the scene on Tuesday.

The ambitious two-stage rail project has a total investment cost of more than 520 billion baht ($15.3 billion).

The 243-kilometer (151-mile) Bangkok to Nakhon Ratchasima segment is expected to be completed by 2028, and the 356-kilometer (221-mile) Nakhon Ratchasima to Nong Khai segment by 2029.

(AP)