A DISGRUNTLED employee at a US beer distributor gunned down eight co-workers after reportedly being called in by bosses for disciplinary action.

Police rushed to Hartford Distributors in Manchester, Connecticut, shortly after 7.30am local time, too late to prevent the slaughter.

The gunman opened fire during a shift change when up to 40 people were inside. The killer’s own body was found about 40 minutes later.

In addition to killing eight, he wounded at least two people, who police said were “expected to survive.”

“There were nine individuals, including the suspect, who were killed during the shooting,” said a police statement. “We are presently in the process of trying to identify the victims and make notifications to family members.”

The local Hartford Courant daily said the shooter was 34-year-old warehouse driver Omar Thornton and that he had been called in for a hearing just before the shooting rampage began.

“The union was bringing him in to meet with the company to remedy the problem,” said John Hollis, a Teamsters union official was quoted as saying. “He started shooting.”

It was unclear what the nature of that hearing was, but some US reports suggested Thornton had been fired.

“Something snapped inside his head,” his ex-girlfriend told a local CBS television affiliate. “He’s never been violent that I know of,” she said. “I don’t know what happened inside of him.”

Other unconfirmed reports from family members suggested Thornton, who is black, had complained about being racially harassed at work and that his superiors had done nothing about it.

The Hartford Courant quoted sources saying that Thornton had used a .223 caliber semiautomatic rifle and that two of the victims were shot outside and the rest inside, where he was later found.

“Our prayers go out to the employees and families of the victims. In the wake of this tragedy we are all left asking the same questions. How could someone do this? Why did they do this?” said Connecticut Governor Jodi Rell.

“It was a senseless act of violence that has left us all shaken and reminds us just how precious and fragile life truly is.”

Among the wounded was reportedly Steven Hollander, whose family owns Hartford Distributors, the biggest Budweiser distributor in Connecticut with some 400 employees.

“Everyone is devastated by this tragic and senseless act,” Jim Bataglio, a spokesman for the Hollander family, was quoted as saying in the Hartford Courant.

Many US states have loose gun ownership laws and massacres in public places are a regular occurrence.

In June, a man involved in a domestic dispute opened fire in a Miami area restaurant, killing four women and wounding three others before taking his own life.

In early January an angry employee at a Missouri power plant shot dead three people and wounding five others, before killing himself. The bloodshed was believed to have been triggered by a dispute over his pension funds.