MINNEAPOLIS — Minnesota Gov. Tim Walz said Friday he is considering placing a 30-day hold on a metal recycling company’s permit after a fire that burned for days and sent up plumes of smoke.

Speaking at a forum organized by the University of Minnesota’s Humphrey School of Public Affairs, Walz said he is looking at ways to hold Northern Metals responsible for pollution caused by this week’s fire at its plant in Becker, in central Minnesota.

Walz told the audience that he does not trust Northern Metals “to do the right thing,” KMSP-TV reported. The Democratic governor said state regulators would make the decision on a 30-day hold.

The Becker Police Department reported in a Facebook post that initial air tests have found no hazardous chemicals. The Minnesota Pollution Control Agency took additional air samples Thursday; results were expected Friday.

Northern Metals did not immediately return a phone call from The Associated Press for comment Friday. But state Sen. Andrew Mathews of Milaca, whose district includes Becker, said in a statement Friday that Northern Metals “is fully cooperating” with the state fire investigation, the MPCA and local public health officials.

“To suggest an arbitrary 30-day hold on permitting from the state is irresponsible and an overreaction,” Mathews said.

A state fire marshal investigator was at the scene Friday. The cause of the fire is still under investigation.

Police said Thursday that firefighters had the blaze under control, but the fire flared late Thursday, sending more smoke over Becker. Classes in Becker were canceled Thursday but resumed Friday.

Residents of the city of 4,500 people have not been asked to evacuate, but should stay away from the immediate area of the fire, police have said. Becker is about 50 miles (80 kilometers) northwest of Minneapolis.

Northern Metals moved its shredding operation from Minneapolis to Becker last year after the Pollution Control Agency ordered it shut down because of high levels of air pollution and inaccurately recorded pollution.