Engineers worked through the night to attempt to make southbound lanes on a fire-damaged section of the M1 motorway safe to reopen to traffic by Monday morning.
Two lanes on the northbound carriageway have already been reopened but Roads Minister Mike Penning urged motorists to avoid the route as congestion was expected.
The full width of the motorway between junctions one and four may not reopen until “the middle to the end of next week”, he told Sky News.
Motorists have faced traffic chaos since a blaze ripped through a scrapyard under an elevated section of the motorway on Friday morning, causing significant damage to the bridge’s structure.
Engineers were working to erect a temporary structure under the bridge to give it the stability necessary to carry the weight of traffic.
The Highways Agency said that one southbound lane should reopen overnight and they hoped that a second could be reopened on Monday morning.
Mr Penning said: “We are working as quickly as possible to reopen lanes on the M1. However safety has to be paramount.
“As a former firefighter I know first-hand the intensity of fires of this kind. I’ve seen the damage to the bridge and it should not be underestimated how significant it is.”
He said police were investigating what was stored at the scrapyard and how the incident took place.
Transport Secretary Philip Hammond told BBC1’s The Politics Show that the government would “have to look very carefully at what kind of activities can take place under elevated motorways”.
He said: “Once we’ve seen the scale of impact that a fire can have in a scrap yard under a motorway, I think everybody would agree it is inappropriate to have scrap yards under elevated motorways and we will have to take action to ensure that inappropriate uses are eliminated under motorways.”