US police are hunting a gunman who shot dead three people and wounded five others in a rampage at the Missouri offices of a Swiss power company.
Police Captain Sam Dodson confirmed that three people had been killed in the shooting spree which began at the start of the morning shift when a man armed with an assault rifle and a handgun stormed into the offices.
Dodson could not confirm reports on the local KTVI Fox news channel that the shooter -named by police as 51-year-old Timothy Hendron - was among the dead.
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Five other people were wounded, three of them were in critical condition, a St. Louis spokeswoman said.
Police SWAT teams entered the offices of ABB Power after reports of the shooting spree at the busy factory, which employs 270 workers, located in an industrial area of the city.
"There is a large business at this location with numerous employees inside of the building," a police spokeswoman said.
Gunman 'unaccounted for'
"The shooter is thought to be at this location, but he is currently unaccounted for."
Local media reported some employees had sought refuge on the roof of the building to escape the gunman, and were talking to police.
"We believe (the suspect is) in the complex right now. That's why are tactical (teams) are going room by room. It's a very large complex, very compartmentalized," said Dodson.
"It's a very large complex and it's connected to an even larger complex so it's a very slow and methodical process and it will take several hours."
He added there was no indication there was more than one shooter, and confirmed he was believed to be a former employee.
"The suspect was armed with an assault rifle and a hand gun and the whole complex was involved in the shooting from the exterior to the interior," Dodson added.
According to Kansas City court documents, Hendron was involved in a legal dispute with the firm over the management of employees' retirement funds.
ABB spokesman Bob Fesmire could not confirm whether the shooter was a former employee.
Assault rifle, handgun
"We can confirm that there was a shooting, but the information is still unclear," he told AFP.
Fesmire said there would normally be around 100 people in the factory from the start of the first shift at around 6:00 am to 6:30 am.
But he added there were fewer workers at the plant on Thursday thanks to a blizzard and temperatures which plunged to 12 degrees Fahrenheit (minus 11 Celsius), forcing some colleagues to stay at home.
Police said about 40 to 50 workers were inside at the time of the shooting at the beginning of the shift.
The plant is part of Zurich-based ABB's engineering business, and makes power transformers.
In a statement issued from Zurich, ABB said: "This is obviously a very serious situation and we are working to gather more information as it becomes available.
"The welfare of our employees is of utmost importance to us."
