Traffic queued for miles on the M25 after a lorry carrying bleach exploded, blowing debris across the motorway.
The lorry exploded at about midday
On one stretch of the London orbital, both carriageways were shut after the load of hydrogen peroxide caught fire.
Motorists described hearing a series of explosions and seeing items blown across all 10 lanes at junction 13, the exit to Staines, just before noon.
Two lanes remain shut but it is hoped they will open by Wednesday rush hour. The driver suffered minor injuries.
The closed lanes are on the anti-clockwise section and traffic has been queuing back to junction 16 at the M40.
Drivers stuck in the heat were approached by people selling bottles of water on the stretch of motorway where traffic was at a standstill.
No-one other than the lorry driver was hurt. The wind blew toxic fumes away from the traffic.
Drivers are being told to avoid the area
One driver told BBC London: "There was a huge explosion, I think about three in total, and we saw these blue things which looked like water canisters flying across the road."
The blue plastic buckets were among debris spread across the motorway by the blast, which destroyed the lorry.
Police are investigating why the lorry exploded.
It happened near the junction for Heathrow Airport, and British Airways has said those who missed flights because they were caught up in the tailbacks may be entitled to a refund.
Neil Owen, from Surrey Fire and Rescue, told BBC News: "Looking at the lorry, it's actually sort of totally written-off.
"It's burnt from end to end, but fortunately nobody was hurt."