Police have a road in Hartlepool blocked off and at one point more than eight emergency vehicles were on the scene.
Cleveland police are still on the scene of the incident in the Oxford Road and Richmond Street area.
A spokeswoman for the police said they could not release any details at this time.
A spokesman for the North East Ambulance Service, said: "We got a call at 5.40pm this evening to a report of a possible assault.
"A man in his 20s was taken to the University Hospital of North Tees."
More information to follow.