One person was killed and seven others were wounded by a knifeman in a two-hour stabbing rampage across Birmingham city centre.
The first stabbing attack took place in Constitution Hill, then the attacker moved south stabbing randomly, police officers said.
The stabbings did not appear terrorism related, gang related or connected to disorder, West Midlands Police said.
Police added that there was no evidence the stabbings were a hate crime.
Murder inquiry detectives said they were hunting a single suspect.
The force urged anyone with CCTV or mobile footage to contact them.
“The events during the early hours of this morning are tragic, shocking and understandably frightening,” Ch Supt Steve Graham said.
“It does appear to be a random attack because we haven’t found any links between the victims, either in their nature or in where they were socialising.
“Please be assured that we are doing absolutely everything we can to find whoever was responsible and try to understand what exactly happened.”
Officers earlier found a knife in a drain but Mr Graham said it was “way too early” to say if it was connected to the case.
Prime Minister Boris Johnson thanked emergency services “working hard at the scene”.
He tweeted: “All my thoughts are with those affected by the terrible incident in Birmingham last night.”
The streets in the area had already been closed to traffic due to coronavirus restrictions.
Outside the cordoned-off area, much of the city centre is open as usual.