Witnesses heard several gunshots at a FedEx facility and one said he had seen a man firing an automatic weapon.

The gunman, thought to have been acting alone, is reported to have killed himself. Authorities said there was no further threat to public safety.

Police say several of the injured are in hospital. Flights from the nearby airport are not affected.

"As officers arrived, they came into contact with an active shooting incident," city police spokeswoman Genae Cook said, adding that it had taken place at around 23:00 local time (03:00 GMT).

"After a preliminary search of the grounds, inside and out, we have located eight people at the scene with injuries consistent to gunshot wounds. Those eight were pronounced deceased here at the scene.

Ms Cook said four of the injured had been transported to hospital, one in a critical condition. Many others were treated at the scene or themselves sought treatment in hospital.

She said the motive for the killing was unclear.

Ms Cook paid tribute to the officers involved.

"It is very heart-breaking and, you know, in the Indianapolis Metro Police Department, the officers responded,... they went in and they did their job," she said.

"And a lot of them are trying to face this because this is a sight that no-one should ever have to see."

'Sub-machine gun'

A FedEx statement said the company was aware of the shooting and co-operating with the authorities.
"Safety is our top priority, and our thoughts are with all those who are affected," it said.

Local media quoted FedEx worker Jeremiah Miller as saying he had seen the gunman firing.

"I saw a man with a sub-machine gun of some sort, an automatic rifle, and he was firing in the open. I immediately ducked down and got scared," he said.

Last week, President Joe Biden announced his first steps since taking office to tighten gun controls following a series of mass shootings.

It includes efforts to set rules for certain guns, bolster background checks and support local violence prevention.

The Gun Violence Archive puts the number of gun violence deaths from all causes at 12,395 so far this year in the US, of which 147 were in mass shootings. Last year saw a total of 43.549 deaths, and 610 in mass shootings.