The incident occurred at the coarse ore stockpile shed within the concentrator precinct at about 11am on September 17.

The man was treated by paramedics at the scene and transported to the Karratha Health Campus in a critical condition. He later succumbed to his injuries.

A CITIC Pacific spokesman said support was being provided by his direct employer.

"We're currently directing our efforts to helping those affected at site, including provision of counselling and managing the incident under the guidance of relevant authorities," he said.

"We extend our deep condolences to the man's family and workmates and will work closely with investigators to determine the cause of this tragedy."

WA Police and the Department of Mines, Industry Regulation and Safety are investigating.

A DMIRS spokesman said the department had sent safety inspectors to site.

"Our thoughts are with those affected by this tragic event," he said.

A statement on the Construction, Forestry, Mining and Energy Union Facebook page said the deceased worker was a scaffolder.

"There's a report that crane operators on site have been instructed by their group leaders to lower their booms at 11am [on September 18] for 10 minutes as a mark of respect," the statement said.

"We encourage everyone on site to pause today to think about safety and consider what more you can do to make sure we all go home to our families at the end of each swing."

CFMEU organiser northwest Phil Kennedy has been sent to the site.