An off-duty police officer and paramedic were sprayed in the face with an unknown corrosive substance after stopping to help at the scene of a major car fire.

The pair joined other 'Good Samaritans' in lending a hand after a stolen car was involved in a serious collision with a lorry at around 7pm on Friday night.

The vehicle crashed into the a metal barrier at the side of the M11 near Chigwell and Loughton in Essex, before bursting into flames.

Just minutes before collision, police had been alerted to the blue VW Golf being stolen from outside a nearby shop.

The victim in the car theft, a man in his 20s, reported that one of the men held a knife in his hand. Less than 10 minutes later, the stolen car collided with the lorry on the M11, southbound, between junctions 5 and 4.

The car caught fire and after seeing the incident, passing drivers stopped to help.

Following the collision, the drivers of the stolen car left the vehicle and sprayed an unknown substance in the faces of two people who were among those who had stopped to assist.

One was an off duty paramedic, the other, an off duty police officer.

The suspects then stole another car - a white Vauxhall Astra - at the scene of the collision to make their getaway.

This car was later recovered in Dagenham, East London.

Police said medical treatment was received by the two people who were sprayed with the unknown substance, and it is not believed they will suffer from any long term effects.

Two ambulance crews, a rapid response vehicle and response car from Essex and Herts Air Ambulance were dispatched to the scene. Both men sprayed with the substance were taken to hospital for further care.

Their conditions are not believed to be serious or life-threatening. The driver of the lorry was uninjured.

Kevin Brown, Director of Service Delivery at The East of England Ambulance Service NHS Trust (EEAST), said: 'This unprovoked attack on two Good Samaritans who were trying to help at the scene of a road traffic collision is deplorable.

'Sadly they were in the wrong place at the wrong time and we wish them a speedy recovery.'

The crash caused disruption to drivers, but the lane reopened later that evening following forensic recovery of the vehicles.

One suspect was described as Asian, and between 25 to 30 years old. He had a dark beard, and was wearing a baseball cap, a navy blue buttoned top, and dark coloured bottoms. He also had a small, black leather bag with him.

The other suspect was described as white, with short dark hair.