Freezing fog has gripped the south of England, prompting warnings for travellers to exercise “extreme caution” as at least 17 people were injured after a coach overturned on a road in Oxfordshire.
The AA warned of the “worst possible conditions” for motorists as the heavy fog combined with sub-zero temperatures.
The Met Office issued a yellow severe weather warning – meaning ‘be aware’ – for London and the south east, south west England, the east of England and the Midlands.
However, fog was also observed as far north as the Humber.
Visibility could be as low as 100 metres in affected areas and ice could develop on the roads.
The Met Office said poor visibility could persist into Friday afternoon.
"The main thing we have had is large, dense freezing fog patches,” said Met Office meteorologist Emma Sillitoe.
"People driving around in the morning should take care on the roads."
The fog is set to lift and thin slowly and could linger into the late morning and early afternoon, particularly in the South East and East Anglia, the Met Office said.
The AA warned motorists to allow for extra travel time, to ensure their car tyres are properly inflated and that windscreens adequately de-iced.
"We have got the worst possible conditions really, of fog and icy roads, and that can be lethal,” said AA Spokesman Ian Crowder.
"I think the message is extreme caution and to prepare for the worst and make sure all windows are clear."
In the early hours of Friday, 17 people were hurt when a coach veered off a motorway slip road and overturned while driving through the fog at junction seven of the M40, near Milton Common in Oxfordshire.
The driver and 16 passengers suffered injuries including broken bones, cuts and bruises.
South Central Ambulance Service (SCAS) said "thick fog" had made access to the scene more difficult and Thames Valley Police said the road was to close for several hours.
An SCAS spokesman said: "South Central Ambulance Service declared this a major incident due to the number of patients involved and attended the scene with our colleagues from Thames Valley Police and Oxfordshire Fire and Rescue Service.
"There was thick fog in the area at the time of the accident which also presented challenges to the emergency services getting to the scene."
Six ambulances helped take the 17 casualties to the John Radcliffe Hospital in Oxford.
The crash happened just 20 miles from a fatal pile-up on the A40 in similarly treacherous conditions on Wednesday morning.
Additional reporting by agencies.
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