Nine people have been killed after a gunman wearing body armour opened fire outside a bar in the US in an attack which lasted under a minute.

At least 27 people were injured during the massacre in Dayton, Ohio, which took place at around 1am local time this morning (6am BST). In total 15 have been discharged from hospital and five remain critically injured.

Police were called to Ned Peppers, a bar in the down town Oregon District of the city, to reports of an active shooter.

Assistant police chief Matt Carper told reporters the suspect, who had a .223 calibre automatic rifle with a high-capacity magazine and fired multiple rounds, had been shot dead by officers.

He added: "There is one shooter we are aware of. We are working to identify him to see what his motivation was.

"The FBI are on the scene assisting but we are leading the investigation."

Mayor Nan Whaley later confirmed the suspect had additional magazines and was wearing body armour. He has been identified but his details have not yet been made public.

Police confirmed on Twitter there were officers in the area at the time of the incident and they were able to "put an end to it quickly".

Footage and images from the scene show emergency vehicles outside the bar, which is in Dayton's arts and entertainment district.

Clips posted on social media purported to show several bodies in the street outside the bar and one witness claimed he heard up to 50 shots and saw people "trampling over each other".

Another witness who was five foot away told WHIO-TV news network it was the "scariest moment of his life" when the masked and hooded gun man opened fire.

Popular tiki bar Ned Peppers posted on Facebook that all of its staff were safe and said "our hearts go out to the the victims".

It later added staff were "shaken and confused" and that the "shooter started down the road and made his way towards the business where police are usually based."

They added it was a "senseless act of violence" and they "do not know when the area or business will open".

Asst police chief Carper added it was a "very short time line of violence" and that he was not aware of any remaining threat to the public.

He said: "This is unheard of and very sad. This is a tragic day.

"We're very fortunate that the officers were in close proximity and that they reacted in the way they did and as bad as this is it could have been much, much worse."

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Witness James Williams wrote on Facebook: “It happened right in front of the patio where I was sitting in front of Neds.

"[The shooter] tried to go into the bar but did not make it through the door someone took the gun from him and he got shot and is dead.

"There are at least eight people dead right by the picnic table where I was at on street. A bunch of people was [sic] taken to the hospital I don’t know how many this place is a disaster.”

(Image: WHIOtv7)

Mayor of Dayton Nan Whaley posted on Twitter: "I’m heartbroken. Thank you to our first responders for all that you’ve done. We will share updates as we have more information."

She told reporters: "I'm amazed by the quick response which saved hundreds of liives.

"People went home wanting to enjoy their Saturday night and get home safe and some of them didn't."

She added that the group of victims was diverse.

A vigil will be held at 8pm for the victims and the street will open this afternoon as usual.

Singer Lizzo has said it was a "close call" for her family.

She wrote on Twitter: "Just got off the phone w/ fam in Dayton... it was a close call for them but that's not the case for 9 other families between this & the terrorist attack in El Paso & recent other shootings.

"I feel completely helpless.. make noise & bring awareness.. vote.. don't normalize this."

The incident came just hours after 20 people were gunned down at a mass shooting in El Paso, Texas.

A further 26 people were wounded during the shocking attack at a Walmart in the south of the country. The shooting is the eighth worst in US history.

It happened just a few miles from the Mexican border and saw three Mexican nationals killed and six injured.

Police are investigating whether an anonymous white nationalist manifesto published online and claiming the massacre targeted the Hispanic community is legitimate.

A 21-year-old named as Patrick Crusius and from the city of Allen, about 10 hours from El Paso, is in custody.

It's the latest in a series of mass casualty killings in the US involving guns.

This year alone there have been 250, resulting in more than 1,000 casualties.