A pregnant woman is fighting for her life after being stabbed in Sutton Coldfield.
The 40-year-old was taken away from the scene by air ambulance at around 4pm.
A 41-year-old man was immediately detained in connection with the attack after the incident in the busy town centre, West Midlands Police said.
Two members of the public - both men - suffered minor injuries after intervening and are being treated.
Julian Harper, West Midlands Police force incident manager, said: "This happened in a busy area but I would reassure the community that a man has been arrested and we are working hard to understand the circumstances that led up to the assault.
"What is clear at this early stage is that two members of the public bravely stepped into what was a dangerous and volatile situation, with complete disregard for their own safety and I commend them for their actions. Fortunately they suffered only minor injuries."
Anyone with information about the incident is asked to call police on 101 or Crimestoppers anonymously on 0800 555 111.
A police spokesman confirmed that the man - who was arrested on suspicion of attempted murder - and the victim are known to one another.