A man has been arrested on suspicion of raping three women and sexually assaulting another in a two-hour period in Manchester.
The incidents involving street sex workers took place in the Fairfield Street area of the city centre between 8.30pm and 10.30pm on Tuesday.
A 33-year-old man was arrested on a bus heading out of the city shortly after the last reported attack, police said.
The first incident in North Western Street, was reported at around 8.40pm. A short while later, at around 9pm, a second incident was reported off Palmerston Street.
Later at about 10.20pm a third incident was reported in Betley Street, followed shortly by the final incident which happened near Every Street.
Chief Superintendent Russ Jackson, of Greater Manchester Police, said: "These are very serious sexual attacks involving violence and we are very seriously concerned. Thankfully none of the women suffered serious injuries but they are understandably traumatised.
"We are working closely with specially trained officers to obtain their accounts so that we can bring the person responsible to justice. The women describe themselves as sex workers and we are treating these incidents as clearly linked attacks upon them.
"It is absolutely vital if anyone witnessed any of these incidents or saw a man acting suspiciously in the Piccadilly Trading Estate from around 8pm till 10.30pm last night that they contact police.
"I implore anyone who knows anything about these attacks to come forward. I assure you our focus is purely on identifying the attacker."
Anyone with information should contact police on 101 or Crimestoppers anonymously on 0800 555 111.