A construction worker has died after he was crushed in a cherry picker accident at a coal mine site in northwest NSW.

A construction rigger who died while working on a cherry picker at a coal mine was minutes away from stopping work.

The man, who police say was in his 30s, was working on the construction of a coal-handling plant at Boggabri coal mine in northwest NSW.

Reports about how the man died vary but it appears he was working on a cherry picker when he was hit by a piece of machinery on Wednesday morning.

Construction, Forestry, Mining and Energy Union (CFMEU) Newcastle organiser Peter Harris was at the Boggabri coal mine expansion project for a monthly union meeting when he heard people screaming.

“We could see everyone screaming and yelling and trying to do CPR,” Mr Harris told AAP.

“[Paramedics] let us know after 20 minutes that he had died.”

Mr Harris said the man had only about five minutes to go before he would have left the construction site to attend a 9am union meeting.

He said it looked like a mechanical failure prompted the bucket on the cherry picker to tip, hitting the man and breaking his neck.

“The bucket itself, we could see it was leaning over at a precarious level,” he said.

“I have never seen reported the type of mechanical failure that has occurred.

“It is something fairly extreme that has made the bucket drop off the angle it has.”

A police spokesman said the man was crushed between the cherry picker and another structure.

It is understood the man was from Queensland.

“This site has a good safety record, there has never been a serious incident,” Mr Harris said.

Idemitsu Australia Resources is expanding the coal mine, for which Thiess Sedgman has the construction contract.

In a statement Idemitsu said all mining had ceased at the site until further notice.

“We will work closely with our construction contractor to provide the appropriate support and assistance at this time,” the company said.

Counselling is being provided to workers.

CFMEU NSW assistant secretary Rebel Hanlon said the death came on the back of last month’s double fatality at a mine site in the NSW Hunter Valley.

Jamie Mitchell, 49, and Phillip Grant, 35, died after a wall collapsed on them 500m below ground at a coalmine in Paxton on April 15.