A construction worker was killed after he was hit by a steel plate at a worksite near Changi Airport on Wednesday.

The police said they were informed at around 11.45am and found the unconscious man along Airport Boulevard. He was taken by ambulance to Changi General Hospital, where he died.

The police are investigating the unnatural death.

The incident is believed to have occurred at a worksite near the airport's new Terminal 4.

The Ministry of Manpower (MOM) said it has issued a stop-work order to the contractor, Chan and Chan Engineering.

All work relating to excavation has ceased and MOM has started investigating, added its spokesman.

The area was not accessible to the public and was cordoned off, said the spokesman.

A spokesman for the Changi Airport Group said it is assisting the authorities in their investigation.

"We are sorry at the loss of life due to the accident and are working with the contractor to provide assistance to the worker's family."

The Straits Times understands that the worker was from Bangladesh and was building a high tension cable duct at the time.

It is believed that he had been adjusting horizontal struts - which held apart two steel plates as part of the duct's temporary formwork - when one of them gave way. One of the steel plates hit the worker, pinning him against another plate.

It is not known how long he was pinned but his colleagues eventually managed to get him out, ST understands.

The new terminal is slated to open in the second half of this year.