Firefighters, paramedics and police officers also joined the emergency response to the incident in Regency Square, Hove around 12pm.
Sussex Police said officers responded to ‘concerns for the welfare of a man’ at a flat.
A spokesperson added: “He has been taken to hospital with a head injury, where he remains.
“We have no further information at this time.”
A spokesperson for East Sussex Fire and Rescue Service said: “We attended an incident in Regency Square at 11.57am today to support a SECAmb-led incident.”
A spokesperson for South East Coast Ambulance Service said: “This was a call to a private address so not one we would comment on due to patient confidentiality.”
Photos from the scene showed crowds gathering to watch as the air ambulance left the scene.
1. Hove emergency incident
The emergency services responded to a medical incident in Hove Photo: Eddie Mitchell
2. Hove emergency incident
The emergency services responded to a medical incident in Hove Photo: Eddie Mitchell
3. Hove emergency incident
The emergency services responded to a medical incident in Hove Photo: Eddie Mitchell
4. Hove emergency incident
The emergency services responded to a medical incident in Hove Photo: Eddie Mitchell