A man was shot outside the Rainbow Warehouse in Birmingham on Saturday night.
The incident happened just before midnight while Circo Loco In The Arena was taking place at the venue.
The event, which featured Jamie Jones, Seth Troxler, Carl Craig and more, was scheduled to take place across Saturday and Sunday, though organisers cancelled the second day immediately.
Circo Loco issued a statement on Sunday at 2.34am via Twitter which read: "Due to circumstances beyond our control, we have to cancel today's event. We'll have more information on tickets and refunds this week."
The shooting occurred late on Saturday night, just before the event was due to finish. Police confirmed that local officers as well as firearms teams, the force helicopter, police dogs and detectives from Force CID were alerted at 11.47pm.
The injured man received first aid at the scene before being taken to hospital, where he remains in critical condition.
News of the incident spread online after photos of a police cordon outside the venue were posted to Demotix.
It appears that no other people were injured and that the majority of partygoers were left unaffected by the shooting.
Twitter users such as Columbus The Great and Tanita had a positive time at the event:
Circo Loco was sick, wish I could go back and do it all again! #CircoBlues
— Columbus The Great (@CeeOhhEll) August 12, 2013
Circo Loco this weekend was EPIC don't think ive fully recovered though.... #stillhurt
— Tanita (@TanyalovesTatts) August 12, 2013
Mixmag contributor Joseph Patterson was also at the party. He told us: "It was full of people shuffling their hearts out to the sounds of tech house, inhaling balloons while they were at it. Even though there were much more hood folk at this Circo Loco than ever seen before, the vibe was nice and calm: everyone had a smile on their face."
However, other eye witness reports are not so sunny. Matt Brawn, who travelled from London for the event, told us that it was "one of the moodiest raves" he'd ever been to.
"The soundsystems were banging, all the DJs were on point, it was wicked. But I wasn't a fan of the atmosphere... There were loads of people who weren't there for the music, they just seemed to be looking for trouble," he said.
He also informed us that he was not searched on his way into the venue and that no metal detectors or door policy were in place.
Circo Loco In The Arena caused controversy last year by introducing a strict door policy.
In a police statement, Detective Inspector Justin Spanner said: "This is a very serious crime which must have been very frightening for clubbers to witness... The motive for the attack remains unclear but initial enquiries indicate this was a targeted attack and that the gunman escaped on foot.
"We've been working hard to reduce gun crime across the region but crimes like this - no matter how rare they are - tarnish Birmingham's reputation as a great place to enjoy a fantastic night out.
"If we are to understand why this shooting occurred and bring those responsible before the courts, I need anyone who was in the area at the time and has not yet spoken to police to get in touch."
Police are currently looking for witnesses and anyone with more information about the incident. If you have any info, call the police non-emergency number on 101 or the anonymous Crimestoppers line on 0800 555 111.
A police investigation is ongoing.