M4 tunnel fire: Experts begin tests to analyse damage
Tests are being carried out which will help determine how much longer the Brynglas tunnel westbound on the M4 motorway will remain closed.
The Welsh Government said it could reopen next week but experts were still analysing the tunnel's lining.
Motorists are still facing delays of about 30 minutes, with only the eastbound tunnel open with a contraflow system.
The tunnel, near Newport, was closed following a lorry fire on Tuesday.
The Welsh Government said engineers spent Thursday carrying out a full structural, technical and safety inspection while a major clean-up operation continued.
The lorry was removed on Wednesday and overnight high-pressure cleaning was completed to allow works to begin.
All damaged lighting was removed, and lighting in the eastern section was being cleaned, repaired and tested.
The tunnel's lining is also being examined.
A Welsh Government spokesman said: "Engineers have today been carrying out a full structural, technical and safety inspection, whilst the major clean-up operation continues.
"Once these inspections and assessments are completed we will know the full extent of the damage and the work required to bring the tunnel back into use."
"Until that work is completed the westbound tunnel will remain closed and we envisage this work will be completed before the demands of next week's commuter travel commences."
Drivers are still being urged to avoid the motorway, and the Welsh Government has warned people to expect congestion with "four lanes down to two".
On Thursday, drivers reported long delays in the area, particularly with motorists trying to join the M4 from Newport.
A Welsh Government spokesman said: "We'd repeat the message for people to use common sense and try and try and avoid the M4 and use alternative arrangements where possible."
Described as the main artery into Wales, the tunnel was closed on Tuesday morning following the incident at about 0830 BST.
Despite the severity of the blaze, and the chaos that followed, the lorry driver escaped unhurt.
Firefighters spent most of the day tackling the blaze, and black smoke was seen billowing from the tunnel.
Drivers caught in the congestion reported taking up to an hour to travel a mile, with lengthy tailbacks spanning several junctions.
The incident has re-opened the debate on whether an M4 relief road is needed.
Conservative AM William Graham said he had "dreaded" an incident like this, adding: "This is why we were so disappointed when the M4 relief road was cancelled".
Plans for the £1bn road were scrapped in 2009, but the Welsh Government is still looking at previous plans to divert M4 traffic onto a Llanwern steelworks road.
The South Wales Chamber of Commerce said the disruption caused by the tunnel fire could have a significant impact on businesses.
One haulage firm, Hicks Logistics, based in Caldicot, Monmouthshire, said it lost £5,000 of income on Tuesday as a result of lost truck loads - a quarter of the business it does every day.