Seven people were injured, including a 20-year-old woman who is in a critical condition, when a car struck pedestrians in a hit-and-run collision.
The crash happened at 21:50 BST on Thursday during what police described as a "cruise meet" on Europa Way, Trafford Park - an area reported to attract boy racers.
One witness described seeing people get "launched into the air".
Two men, aged 21 and 26, have been arrested.
A blue BMW 330D understood to have been involved in the crash was later found in Salford.
Greater Manchester Police has stepped up patrols in the area, but say there is no evidence the incident was terror-related.
The men have been held on suspicion of causing serious injury by dangerous driving. The 21-year-old was also detained for failing to stop after a collision.
There were 60 vehicles present at the time of the crash, police said.
Ch Supt Wayne Miller said: "We are appealing for anyone with any information, no matter how small or insignificant it may seem, to get in touch as a matter of urgency."
Ryan Currie, 23, from Didsbury, said he saw three people and a dog get "launched into the air".
He said: "The car then drove through them and carried on without stopping.
"Loads of people ran over to attend to the injured."
Trainers could be seen lying on the road and pavement, with purple medical gloves left strewn around.
One man who lives in Trafford Park said "boy racers" were taking part in a car meet at about the time of the incident.
"Little kids in big cars are always racing around the roundabout so something like this is bound to happen."
Parts of the Trafford Park area have stretches of long, straight roads and have become known locally as a place for car enthusiasts.
Jamie Brown saw the crash and knew some of those who were injured.
He described seeing "people flying" and said he placed a girl in the recovery position.
"It was horrible to see. There were bodies lying on the road and people were screaming," he said.
A police cordon is still in place and Europa Way, part of the Trafford Park industrial estate, remains closed northbound between Westinghouse Road and Eighth Street.