UPDATE 1.55pm: A majority of the contract workforce has returned to work at BHP Billiton’s new rail line in the Pilbara this afternoon, after being suspended over safety concerns since Monday.

A BHP spokeswoman said the remaining workforce was expected to start work again tomorrow.

BHP released a statement this morning to say it had temporarily suspended the construction on Monday after raising safety concerns with the contractor – a joint venture between Leighton and Macmahon.

BHP Billiton said in an emailed statement that work was expected to resume in coming days.

"In reviewing the health and safety performance of one of our contractors working on the RGP5 project, we have become concerned that some of the health and safety requirements are not being met,” BHP said.

"As a result, we have asked the contractor to meet our requirements before they recommence work.”

The 200km rail line is being built from Port Hedland to Redmont as part of the mining giant’s Rapid Growth Project 5 (RPG5) to expand iron ore output.

RGP5 will increase installed capacity across BHP Billiton’s Pilbara iron ore operations by 50 million tonnes to 205 million tonnes per annum during the 2011 calendar year.

The company has come under fire for its safety performance in the Pilbara after a string of fatalities this year, but says it has introduced safety initiatives.

BHP and Macmahon have declined to comment on the details of the safety concerns.