A crane at a China-backed high-speed rail project in Thailand collapsed onto and derailed a passenger train on Wednesday, killing at least 22 people and injuring scores, local authorities said.

Footage from the scene verified by AFP showed the crane's broken structure resting on giant concrete pillars, with smoke rising from the wreckage of the train below.

Rescuers worked to extract passengers from the tilted carriages in Nakhon Ratchasima province, northeast of the capital Bangkok. 

"At around 9:00 am, I heard a loud noise, like something sliding down from above, followed by two explosions," said local resident Mitr Intrpanya, 54, who was at the scene.

"When I went to see what had happened, I found the crane sitting on a passenger train with three carriages. 

"The metal from the crane appeared to strike the middle of the second carriage, slicing it in half," Mitr told AFP. 

Thatchapon Chinnawong, the district police chief told AFP 22 people had been confirmed dead and 80 more were injured.

"We are now asking the hospital to say how many people are in critical condition," Thatchapon said.

The accident happened at a construction site that is part of a $5.4-billion project backed by Beijing to build a high-speed rail network in Thailand.

It aims to connect Bangkok to Kunming in China via Laos by 2028 as part of China's vast "Belt and Road" infrastructure initiative.

"A crane collapsed onto a train causing it to derail and catch fire," the Nakhon Ratchasima provincial public relations department said in a statement.

Live footage aired by local media showed rescue workers rushing to the scene, with a brightly coloured train derailed on its side as smoke billowed from the debris.

Thatchapon, the police chief, later told AFP that authorities were pausing the rescue operation due to "chemical leakage" at the scene.

The Nakhon Ratchasima provincial department said the train was travelling from Bangkok to Ubon Ratchathani province.

Transport Minister Phiphat Ratchakitprakarn said 195 people were on board the train and authorities were rushing to identify the deceased.

He ordered officials to determine the cause of the accident, according to a statement.

Thailand already has around 5,000 kilometres (3,107 miles) of railway but the run-down network has long driven people to favour travel by road.

Upon completion of the 600-kilometre high-speed railway, Chinese-made trains will run from Bangkok to Nong Khai, on the Mekong River border with Laos, at up to 250 km/h.

Industrial and construction site accidents have long been common in Thailand, where lax enforcement of safety regulations often leads to deadly incidents.

In 2023, a freight train killed eight people after it struck a pickup truck crossing railway tracks in eastern Thailand.

A freight train killed at least 18 people and injured more than 40 others in 2020 when it crashed into a bus carrying passengers to a religious ceremony.