broken.— Ariana Grande (@ArianaGrande) May 23, 2017
from the bottom of my heart, i am so so sorry. i don't have words.
The star tweeted that she was "broken" over the horrific incident.
Police say they are treating it as a terrorist incident until they know otherwise.
The arena said that it happened outside the venue as people were leaving the concert.
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You can hear what sounds like an explosion in the tweet below:
"Please stay away from the area," the Greater Manchester Police said on Twitter.
Emergency services responding to serious incident at Manchester Arena. Avoid the area. More details will follow as soon as available— G M Police (@gmpolice) May 22, 2017
Police performed a controlled blast on a suspicious device near the site of the first incident, but say that the item turned out to be abandoned clothing.
In another tweet, police say, "Emergency services responding to serious incident at Manchester Arena. Avoid the area."
Social media accounts say a couple loud bangs were heard at the arena where singer Ariana Grande was performing.
EXPLOSION AT MANCHESTER ARENA AND EVERYONE RAN OUT SO SCARY😭 pic.twitter.com/pJbUBoELtE— ♡♡ (@hannawwh) May 22, 2017
There were no immediate details of what happened during the concert by the singer, but witnesses reported hearing two loud bangs coming from near the arena's bars.
"A huge bomb-like bang went off that hugely panicked everyone and we were all trying to flee the arena," concertgoer Majid Khan, 22, told Britain's Press Association. "It was one bang and essentially everyone from the other side of the arena where the bang was heard from suddenly came running towards us as they were trying to exit."
Added Oliver Jones, 17: "The bang echoed around the foyer of the arena and people started to run."
Grande is said to be OK.
Video from inside the arena showed concertgoers screaming as they made their way out amid a sea of pink balloons.
The Mayor of Manchester released a statement on Twitter:
My heart goes out to families who have lost loved ones, my admiration to our brave emergency services. A terrible night for our great city— Mayor Andy Burnham (@MayorofGM) May 23, 2017
(The Associated Press contributed to this report)
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This is a breaking news story and will be updated as more information becomes available. null