Police have set up a cordon in a street on the outskirts of Bradford city centre.
Officers have sealed off part of Spring Lodge Place, Manningham, while the investigation takes place.
One onlooker said: "There are four or five police officers on the scene and there's tape across the road.
"It's complete hearsay, but I've been told there was a fight in one of the buildings within the cordon."
A spokesman for West Yorkshire Police said: "Police are in attendance on Manningham Lane in Bradford following a concern for safety.
"A man has been taken to hospital.
"Enquiries are ongoing to establish the circumstances surrounding the incident."
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