Two people have suffered life-threatening injuries and three have been seriously hurt in a crash involving two buses in Brighton city centre.
The accident happened in Queen's Road, near the Clock Tower, with a Sussex Police spokesman saying: "It has been declared a major incident."
Martin Harris, managing director of Brighton and Hove Buses, said: "We can confirm an incident took place involving two Brighton and Hove buses at about 9.20am in North Street.
"Emergency services are currently at the scene looking after those who might be injured. A full investigation will begin."
A spokesman for East Sussex Fire and Rescue Service said: "Motorists are being advised to stay clear of the Clock Tower area, in Brighton, following a two-vehicle collision involving two buses.
"Firefighters are currently at the scene and there are reports of casualties involved.
"There are two crews from Preston Circus, one crew from Roedean and two crews from Lewes, including the Technical Rescue Unit at the incident.
"East Sussex Fire and Rescue Service were mobilised to the scene at 9.24am and Sussex Police and South East Coast Ambulance Service are also in attendance."