A lorry has plunged off a bridge in England before bursting into flames on to a busy road below.
The vehicle veered off Coleman's Bridge on to the southbound carriageway of the A12 in Witham, Essex, on Wednesday afternoon.
An Essex Police spokesman said: "It is affecting both sides and drivers are asked to avoid the area as the road and the Coleman's Bridge will be closed for several hours and through the rush hour. Drivers are asked to find alternative routes."
Five crews from Essex Fire and Rescue, police officers and an air ambulance are at the scene, and the East of England Ambulance Service said a male patient was being treated.
Joe McCallum, from Essex, arrived in his van on the other side of the carriageway immediately after the crash and said part of the lorry container was on fire.
A photo he posted on Twitter showed a crumpled vehicle on the barriers of the carriageway below, spilling over into the road.
The 28-year-old van driver said he believed it was a lorry carrying frozen goods, but that he could not see anything more due to its "mangled" state.
He said he could not see anybody in the cab following the accident, which happened at around 3.45pm.
The A12 is closed both ways between junction 19 at Boreham and junction 25 by Marks Tey, police said.
Chloe Willis, 20, was in a car travelling to a hockey match with friends and was "about five seconds away" from the accident.
The psychology student told the Press Association "black smoke covered the sky" as the lorry caught fire.
She said: "We had to come to an emergency stop as soon as we saw this lorry turned on its side.
"A big puff of black smoke covered the sky and all the people in cars started to panic.
"You could see where the barriers on the bridge had broken when the lorry had come through."
Ms Willis said the emergency service response was "pretty instant" with numerous fire engines and police vehicles arriving swiftly.
Essex Police appealed for drivers who may have witnessed the accident to contact them on 101.
Highways England said the A12 northbound had reopened but the south side would remain closed for several hours as police continue to investigate.
Motorists are advised to divert by following the A120 toward Braintree at Marks Tey.