A 15-year-old boy suffered serious head injuries when he was hit by an ambulance responding to a 999 call.
The teenager was struck on Lichfield Street in Walsall at about 17:35 BST on Monday and remains in a critical condition in hospital.
West Midlands Ambulance Service said the crew, who were “badly shaken” but not injured, immediately provided care to the boy.
A second ambulance was sent to the original call.
The boy was airlifted to the major trauma centre at Queen Elizabeth Hospital in Birmingham.
The ambulance service said it would be working with collision investigators and providing CCTV footage to determine what happened.
It added: “Our thoughts are with all those affected by this incident.”
Sgt Alan Wood said: “It is important for everyone involved that we piece together the events that led to the collision and I would appeal directly to anyone who saw what happened and has not yet contacted us, or may have caught the collision on a dashcam, to get in touch.”
Follow BBC West Midlands on Facebook, on Twitter, and sign up for local news updates direct to your phone.