Britain has been on high alert after two mass stabbings in London in the a year ago, which saw both perpetrators - convicted extremists released early from prison - shot dead by armed officers.
"We declared this a major incident at the earliest opportunity and we have drafted in scores of officers to help with the investigation and patrol the city to reassure residents and visitors that we are doing all we can to apprehend the person responsible".
Stabbings in England and Wales increased six per cent in the year to the end of March, according to the Office for National Statistics.
Birmingham, one of Britain's most ethnically diverse cities with a population of more than one million, has had an explosive recent history of gang violence.More news: Million West Coast Americans under extreme heat warnings this weekend
He described the suspect as eerily calm, and that "he didn't even run, he just walked" away from his victim until two male bystanders chased him from the scene.
Five others suffered minor injuries in the attacks, which happened at four separate locations in the busy city centre between 12:30am and 2:30am.
Eyewitness Cara Curran, a nightclub promoter, had been working there on Saturday night.
Moreover, the witness also suggested she saw fights between "groups of boys" and heard "racial" slurs.
"I had left with my boyfriend".More news: Daniel Prude: NY Attorney General to set up grand jury
The BBC said the incidents occurred near the area known as the Gay Village in the centre of Birmingham, where many people had been seated at outdoor tables eating and drinking.
David Jamieson, the elected official overseeing policing in the West Midlands, said that people had "a lot of pent-up feelings" because of the pandemic and its impact on their jobs and futures.
He said: "I looked at him, facing him, and I can see he had a blade, small, not very big, and he was stabbing her in the neck".
Television footage showed forensic specialists in protective clothing poring over the scene, which was taped off and guarded by officers.
Earlier in the day, Ch Supt Steve Graham told reporters: "At this stage we believe that the attacks were random and we have no indication of a motive".More news: Steroids Can Fight Severe COVID-19, Multiple Studies Confirm