CHICAGO: A gunman opened fire at a small business in the northern US state of Minnesota, killing four people before turning the gun on himself and dying of a self-inflicted gunshot, police said Friday.

Four other people were taken to hospital, three of whom were in critical condition.

The shooting took place just after 4:30 pm Thursday inside Accent Signage Systems, a company employing about 25 people which makes signs for companies.

“When officers arrived and entered the business to assist with the evacuation of employees, give aid to the victims and to search for the suspect, they found four victims dead from apparent gunshot wounds,” police said in a statement.

Also found dead “was an individual identified as the suspect, it appeared that he died from a self-inflicted gunshot wound,” it said.

The Minneapolis Star Tribune newspaper identified the gunman as a disgruntled former employee who recently had been fired from the company.

It said the owner of the business was among the dead.

Some 458 people were killed in workplace homicides in the United States last year and 242 committed suicide at work, according to preliminary statistics from the Bureau of Labor Statistics.

Two in five women killed at work died at the hands of a relative while robbers accounted for 22 per cent of killings involving female victims and over a third of male victims.

“I deplore this senseless violence,” Governor Mark Dayton said in a statement.

“There is no place for it anywhere in Minnesota. I extend my deepest condolences to the families and friends of the innocent people killed or wounded.”