A footbridge has collapsed on the M20 motorway in Kent after it was hit by a lorry carrying a digger, on one of the busiest travel days of the year.
The motorway is closed between junctions 2 and 4 after the bridge fell onto the London-bound carriageway.
A motorcyclist was hurt but his injuries are not life-threatening.
Travel disruption is said to be severe, with the motorway - the main route to the Channel Tunnel - expected to remain closed until at least midday on Sunday.
Part of the bridge fell onto a second lorry, the driver of which was treated for shock at the scene.
South East Coast Ambulance Service tweeted that a motorcyclist in his 50s had been taken by ambulance to Tunbridge Wells Hospital with suspected broken ribs after the bridge collapsed.
Officers from Kent Police have now left the scene but the force said it "continues to support Highways England in ensuring the motorway is reopened as quickly as possible".
Local roads including the A20 are currently very congested and motorists are advised to avoid the area and find alternative routes if possible.
Witness appeal
The crash happened at around 12:05 BST near the junction with the M26, which links the M25 London orbital with the M20.
Kent Police said it was investigating the circumstances of the crash and appealed for witnesses to get in touch by calling the appeal line on 01622 798538 and quoting the reference 27-0690.
The motorway is the main route to the Channel Tunnel and the Port of Dover for people travelling to France and across Europe.
The crash had knock-on effects across the motorway network after the eastbound M26 was closed to stop further congestion in the area, leading to queues on the M25, which travel reports said was "effectively down to two lanes".
About three hours after the collision, all traffic trapped on the southbound M20 had been released.
Cross-Channel traffic was being diverted on to the A2 and M2 from the M25 and the Port of Dover, Highways England said.
Image copyright Fade Ogunro'Slammed on brakes'
Sonny Gladdish was on the M20 when the crash happened.
He said a lorry carrying a digger was driving on the hard shoulder and made impact with the bridge.
Mr Gladdish said he heard the bang and was about four or five cars behind the collision when it happened.
He said the bridge collapsed on one lorry and he believed the motorcyclist had thrown himself off his bike to avoid the impact.
Another motorist, Fade Ogunro, said: "I was driving down the M20, looked up and slammed on the brakes.
"Across the road a footbridge had literally just collapsed."
She said it landed on two trailers and a motorcyclist and everyone "went into panic mode".
People were unsure about whether to approach the vehicles involved or whether to drive under the bridge on the other side for safety reasons, she said.
"We were all just like in a state of shock. It was something like out of a movie."
Image copyright PA'In pieces'
Witness Andy Sunnucks, 24, a graphic designer who was travelling from Maidstone to Sevenoaks, said: "We are about 15 cars back on the same carriageway as the collision... It looked like a lorry had jack-knifed, and I could see half the bridge was missing.
"We went to have a look and the back end of the lorry was in pieces."
Alex T Magaisa, his wife and two young sons were driving to Gatwick Airport and were just passing the lorry when the bridge collapsed.
He said: "My instinct was just to drive through. My wife saw the bridge falling and there was a big noise. I had to manoeuvre through the debris.
"It was a big shock. It's only just starting to sink in now what might have happened. We were right in the line of fire and we could have been crushed."
Image copyright @emmaraphaelx/PAAnother witness, Sean Fisher, said: "I spoke to [the woman in] the first car behind the lorry. She seemed to be all right. Her daughter was quite brave and went under the bridge and was the first responder to the fallen motorcyclist."
Some drivers also tried to stop traffic on the other side of the road, Mr Fisher said, as they feared the bridge might collapse on the coast-bound carriageway as well.
"At the moment it seems they are going to get the motorcycles out first, the wrong way on the road, and I'm not sure what they are going to do with the cars," he added.
Image copyright Faye OgunroPeople took to social media to share pictures of the collapsed structure.
Helen Ayres posted: "Now that's what I call timing. Just as well the M20 is usually free-flowing on a Bank Holid... Oh. 😣"
Jimmy tweeted: "Couple of guys playing football on the m20; not something you see everyday #m20 #motorway #traffic ..."
Some drivers objected to the handling of the aftermath of the crash, with William Gaunt tweeting: "@kent_police why so long to close M20? 1000s joined 45 mins after bridge strike now trapped."
An estimated 13 million drivers are expected to take to the road between Friday and Monday over the long weekend, according to the AA.
The busiest day was expected to be Saturday, with 10 million motorists expected to travel.
Image copyright @emmaraphaelx/PAAre you near the area of the collapsed bridge on the M20? Email your story to haveyoursay@bbc.co.uk.
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