Officers have set up two crime scenes within a short distance of each other in Birmingham. Newhall Street has been closed to the public between Lionel Street and Fleet Street while there is a large police presence in Temple Row after the incident earlier today.
West Midlands Police said in a statement its officers were called to Temple Row at about 9.50am to reports a woman had been attacked with a knife.
The force said the 26-year-old was taken to hospital where she remains in a serious condition.
A 46-year-old man was detained by police in Newhall Street minutes later after help from members of the public, according to West Midlands Police.
Its statement added that at this stage the force believes it to be an isolated incident and officers are not looking for anyone else.