Previously, SSAB stopped work in part of the area after a number of employees sought medical attention for nausea and headaches.
On Thursday, test results showed elevated levels of toxic gas in the cabins of machines in the area where the new steel mill is being built.
On Good Friday, a new case was first reported, involving a person working outside the area where work had previously been stopped, after which SSAB stopped all work at the construction site.
At 10 p.m., Region Norrbotten announced that two more people were affected.
The person first reported on Good Friday was able to leave the hospital, while the two people announced at 10 p.m. remain in the emergency room, according to the region.
