Boulder supermarket shooting suspect identified as 21-year-old man

Police tape around the car park outside the supermarket in Boulder, Colorado, where the shooting took place (AP/David Zalubowski)

Police have identified a 21-year-old man as the suspect in the killing of 10 people at a supermarket in Boulder, Colorado.

Authorities also identified nine victims after previously identifying a police officer who had been killed. Boulder Police Chief Maris Herold said the victims ranged in age from 20 to 65.

The shooting at the crowded supermarket sent terrorised shoppers and workers scrambling for safety and stunned a state and a nation that has grieved several mass killings.

Ten people were killed in the shooting (AP/David Zalubowski)

Mr Herold said police engaged in a shootout with the suspect inside the supermarket and that is when officer Eric Talley was killed.

The suspect is undergoing treatment at a hospital and is expected to be booked into the county jail, said Boulder County district attorney Michael Dougherty.

Mr Dougherty said investigators do not know yet why the suspect opened fire inside the store. He said the investigation is in its early stages.

A law enforcement official briefed on the shooting told The Associated Press that the gunman used an AR-15 rifle, a lightweight semi-automatic rifle. Officials are attempting to trace the gun.