A man armed with a pump-action shotgun sprayed bullets around a crowded US shopping mall last night, killing five people before being gunned down by police in a children's clothing store.

Terrified shoppers at the Trolley Square mall in Salt Lake City watched helplessly as the man, dressed in a trenchcoat, fired shots around the building at around 6.45pm local time (2.45am GMT).

The incident caused havoc and horror in the two-storey mall - a refurbished trolley-barn filled with winding corridors - as members of the public ran for their lives and eye-witnesses reported seeing bodies of dead and injured people piled up.

More than three hours after the man had been cornered and killed, police were still reportedly searching the mall for shoppers who were found cowering in stores.

"We have six fatalities and multiple victims at hospitals," Robin Snyder, a Salt Lake City police detective, said. "They were found throughout the mall."

At least four people are in hospital, three in critical condition and one in serious condition, it was reported.

Barrett Dodds, 29, an antique store owner, said he saw a man in a trenchcoat exchanging gunfire with a police officer outside a card shop. He added that the gunman was then backed into a children's clothing store before being shot dead.

"I saw the cops go in the store. I saw the shooter go down," he said.

Barb McKeown, 60, of Washington, was shopping at another antique store when two frantic women ran in and reported gunshots.

"Then we heard shot after shot after shot - loud, loud, loud," Ms McKeown added. She and three other people hid under a staircase until it was safe to leave.

Amid scenes of chaos in the aftermath of the shooting, streets were blocked outside the mall as police officers cordoned off the building and surrounding area. Dozens of stunned people were seen standing on the pavement, many wrapped in blankets