Firefighters and police officers were called to North Manchester General in Crumpsall after one of the victims rushed there with burns to his face.
The A&E department was closed, and part of Collyhurst police station was also shut after a second victim went there. Both buildings were later reopened when it was discovered that the powder was harmless.
Four men have been arrested and police say that because black men were targeted in the attacks, they are treating them as racially aggravated incidents.
The scare began when taxi driver Kalu Amah was sprayed as he sat in his cab near Harpurhey market. The powder burned his face and he rushed to North Manchester General.
Bosses there were informed and they immediately closed the A&E department, shortly after 3pm yesterday.
Twenty patients and ten staff were quarantined in the ward while tests were carried out on Mr Amah and his clothing.
The incident came after reports that a man had also been covered in powder in Jersey Street, Ancoats, just after 2.30pm.
And in a third case a man reported being targeted in Blueberry Avenue, Moston at 5.40pm.
One of the men went to Collyhurst police station to report the incident and part of the station had to be closed while tests were carried out. Mr Amah, 42, from Moston, was treated at the hospital and later released. He told how he was sprayed by a group of youths in a car.
He said: "My windows were down, and a blue Ford pulled up beside me.
"I thought the driver was going to ask for directions, but before I knew it they sprayed me in the face with something.
"I saw two black pipes, but it all happened in a second. It was powdery and white, all over my face. My eyes and nose were burning.
"It not only wasted my time and money, they wasted the time of the ambulance, police and fire brigade.
"I’m really angry about it. People don’t realise what they are doing."
Sadie Kirkham, 45, from Harpurhey, was in North Manchester General’s A&E with her husband as he waited for a back X-ray. Mrs Kirkham said: "We were then told there was a major chemical incident and we all had to be locked in for our own safety.
"Some people who had nipped outside for a cigarette couldn’t get back in to see their children. We didn’t know what on earth it was. It could have been anthrax or anything. I think they did the right thing in keeping us in."
Watch commander Ian Hanley said that tests had revealed the chemical was from a fire extinguisher and not dangerous.
The four men arrested were detained on suspicion of causing grievous bodily harm with intent and remain in police custody.
Detective Inspector Alex Nicholson said: "We believe there are other victims out there who have had powder thrown onto them. While it is important they seek medical advice it is equally important they call the police.
"The vast majority of victims were black men and we are treating this as a racially aggravated series of attacks."
Anyone with information is asked to call police on 0161 856 3540 or call the independent charity Crimestoppers anonymously on 0800 555 111
Manchester Evening News
