Traffic chaos after M4 Brynglas tunnel lorry blaze
The M4 has been closed in both directions in south-east Wales after a lorry caught fire in the Brynglas tunnels at Newport.
The Welsh Government said because of the severity of the fire the tunnels will have to remain closed until "a full and thorough" investigation.
Witnesses reported hearing explosions inside the westbound tunnel.
The closure brought traffic disruption during the morning rush hour on one of the key commuter routes in south Wales.
The road was closed in both directions between J24 A48 / A449 (Coldra) and J28 A48 / A4072 (Tredegar Park) and a diversion was set up.
Traffic was directed via the south of Newport on the A48 Southern Distributor Road.
Firefighters were called to the scene at about 08:30 BST, said South Wales Fire and Rescue Service.
Six crews from Maindee, Malpas, Cwmbran, Duffryn and Caerphilly have attended the incident.
The service said no other vehicles were involved in the fire. The lorry driver got out safely and there were no injuries, a spokesman added.
Incident commander Adrian Moyes of South Wales Fire and Rescue Service said crews faced large volumes of black smoke coming from the western side of the tunnel.
"One lorry was well alight on arrival and crews were immediately employed to ensure no persons remained within this or any other vehicle within the tunnel," he said.
"They then proceeded to tackle the blaze and are bringing the incident under control."
Mr Moyes added that following liaison with other partner agencies the incident was being quickly dealt with.
The Welsh Government said emergency services needed the tunnels to stay shut until an investigation and structural examination are completed.
"While these delays will undoubtedly cause inconvenience to motorists, the safety of road users and emergency staff must remain paramount," said a spokesman.
BBC Wales reporter Alun Thomas described the scene at 11:25 BST as "eerily quiet". He said smoke was still coming out of the tunnel and fire crews were still in attendance.
At a nearby hotel, eyewitnesses reported seeing dark clouds billowing from the tunnel just after 09:00 BST.
"There was a lot of black smoke," said Lowri Morgan, receptionist at the Etap hotel, which is situated on the west side of the tunnels alongside the eastbound carriageway.
"Start Quote Gridlock on the M4 at Newport. Haven't moved for 45 mins. Would have appreciated some warning from south Wales police...." End Quote Alun Davies AM via Twitter
"I didn't know anything had happened until a guest mentioned it to me.
"I went up to the top of the hotel and all you could see was the thick black smoke. It was rising above the level of the lampposts.
"It's easing off a bit now as the fire brigade are there. We heard a fire engine arrive."
Traffic Wales reported that the fire appeared to have blacked out cameras monitoring the road in the area.
Lengthy traffic tailbacks have been reported on the M4 and adjacent routes in the area.
Among those caught in the queues was agriculture minister Alun Davies, who tweeted: "Gridlock on the M4 at Newport. Haven't moved for 45 mins. Would have appreciated some warning from south Wales police...."
Another, Buddug Cole, was travelling with her husband and two children, from Cardiff to Heathrow airport to catch a holiday flight to Seattle, USA, when they were caught in the disruption.
"We travelled two miles in about two hours," she said. "We know we are not flying today basically, even if we had a free run from here."
Another motorist said she had taken 1hr 45min to travel from J23 at Magor to J24 at the Coldra.
The motorway was also temporarily closed in February when a car caught fire in the westbound tunnel.