Thiess had earlier announced that it was suspending the night shifts because atmospheric conditions at night might be compounding the gas issue but this did not apply to the two draglines, which are continually monitored.

But the escalating problem had prompted unions to extend the suspension.

“Following Thiess’s cease operations of all but draglines, there were two more workers gassed and sent to hospital to which I have issued a cease operations order on the whole mine during the hours of darkness,” Construction Forestry Mining Energy Union’s industry safety and health representative Tim Whyte told ILN.

The CFMEU met with its members last Sunday about the status of the mines and their concerns, CFMEU Queensland district president Stephen Smyth told ILN .

“The gas incidents at Collinsville are a concern,” he said.

“The safety record of Thiess it has taken a hammering over the last few years at the mine. It won’t be helped by these ongoing matters and effective action needs to occur.”

Last month five Thiess employees at Collinsville were checked in with symptoms of exposure to hazardous gases and a further nine people working in the vicinity were taken to hospital as a precaution.

The situation worsened last week when another 11 of its employees had to be checked into hospital. With the latest two more workers being gassed, the total number of workers who have had to check into hospital has grown to 27.

A Queensland Department of Employment, Economic Development and Innovation spokesman said the mine was already operating under a directive issued by the Queensland Mines Inspectorate on February 24 in relation to gas fume issues at Collinsville.