Ten people died after two different gunmen went upon simultaneous killing sprees on opposite sides of America.

In Salt Lake City, Utah, a teenager armed with two guns opened fire on shoppers in a mall on Monday night, killing five and wounding four others before being killed by police. Meanwhile, a second man shot four people at a business meeting in Philadelphia, then took his own life.

Police in Utah yesterday were still attempting to understand why the 18-year-old, who lived locally, began firing a shotgun indiscriminately in the Trolley Square shopping mall.

The victims, who were found scattered throughout the twostorey mall, included two 28-year-old women, two men aged 52 and 24, and a 15-year-old girl. Four others were wounded, two critically.

Shoppers and staff barricaded themselves in stores or hid in storerooms and under stairwells from the killer, who was wearing a trench coat and also armed with a handgun.

Marie Smith, a store manager, made eye contact with the teenager just before he raised his gun and shot a young woman.

She said, “His expression stayed totally calm. He didn’t seem upset or like he was on a rampage.”

Matt Lund and his wife, another shop manager, sheltered in a storage room for 40 minutes, from where they could hear the violence.

He said, “We heard them say, ‘Police! Drop your weapon!’ Then there was a barrage of gunfire.”

The Philadelphia shootings happened at a business park and were sparked by a dispute over money, said police.

The gunman, armed with a handgun, killed three men and critically injured a fourth before exchanging fire with police and then turning the gun on himself.

Police said they found a scene of “utter chaos” in the boardroom of Zigzag.net, a marketing company.

Two victims were on the floor and another was slumped in a chair. All of them bore gunshot wounds.

Two other men were unharmed but had been bound with duct tape.

The victims were directors of the company, and police believe the gunman had been an investor.