Ten people are in hospital after shots were fired in the Moss Side area of Manchester, police say.
A large number of both armed and unarmed officers attended Claremont Road at about 2.30am after reports of gunshots.
Police say some of those hurt have suffered major injuries in what they called a dangerous attack.
A Caribbean Carnival earlier in the day had brought large groups of people to the area, with several after parties understood to have taken place in Claremont Road.
It is not known whether the carnival, which was due to take place across the entire weekend, will still take place today.
Footage reportedly showing the aftermath of the incident was posted on twitter, with the caption: Shooting at Manchester Moss Side post carnival street party.
The dark video posted on UK Rap’s Twitter page appears to show a panicked group of people being helped by police.
As a voice cries out, shouts of move can be heard, while another voice asks can you hear me.
Give us some space guys can also be heard in the background, while another voice says, are you dumb? as the camera pans around.
Detective Superintendent Debbie Dooley said: We currently have a number of people in hospital all being treated for different injuries but thankfully most do not appear to be life-threatening at this time.
Officers are trying to establish exactly where this incident took place and who is responsible for such a dangerous attack.
Officers are now on the scene establishing exactly where the shooting took place and identify those involved.
Superintendent Dooley said: The area is being searched and examined while we are also trying to speak to as many people as possible and are reviewing CCTV to get all the facts.
Extra police have been sent to the area, which is around two miles south of Manchester city centre.
Anyone with any information should call police on 0161 856 4166 quoting incident number 297 of 12 August or the independent charity Crimestoppers anonymously on 0800 555 111.
(c) Sky News 2018: Ten in hospital after Manchester shooting