A stretches of the M25 in Essex was closed after a pedestrian was in a crash with a car, and the M26 in Kent was shut because a lorry caught fire.
Both emergencies caused long delays and traffic tailbacks on the motorways.
Emergency services rushed to the scene of a collision involving a pedestrian between junctions 29 and 28 on the M25 in Essex, thought to have happened around midday.
The M25 in Essex was closed anti-clockwise between J29 for Hornchurch and J28 for the A12, near Brentwood after a serious collision, National Highways said.
The closure was causing delays of about an hour and 20 minutes and traffic jams stretched back around five miles, the experts said.
The tailbacks on the anti-clockwise carriageway of the M25 reached the Dartford Crossing, Essex Live reported.
Essex Police and other emergency crews rushed to the area, and traffic officers were there to manage vehicle flows.
Traffic was queuing back towards J30 with Lakeside Shopping Centre and the A13, and to J27 with the M11.
Drivers were being advised to follow diversion symbols.
By 8pm, there were delays of an hour-and-a-half anti-clockwise and of half an hour clockwise, National Highways East said.
In a separate incident, in Kent, a lorry fire forced the closure of the M26 eastbound between the M25 J5 for Chipstead and J2A near Wrotham Heath for several hours.
The Fire and Rescue Service were called to the blaze, leading to the closure of the nearby M26 eastbound.
Traffic was backed up for about 12 miles, causing delays of about an hour.
Fire crews said they sent four engines and a bulk water carrier.
Traffic-monitoring site Inrix reported long queues of traffic stuck behind the lorry.
The motorway reopened around 3pm.
But meanwhile drivers on the M25 going anti-clockwise from Surrey were advised to stay on the M25 to junction three and then take the next turning off, the M20 eastbound.
