Swiss rescue workers warned it could be Monday before they are able to reach the accident scene in the Gotthard Tunnel.
Some 113 people are still missing, but Swiss police are optimistic that the death toll will not rise beyond the 11 bodies already recovered.
"We have good reason to believe that we will not find any more victims in the burned-out cars," a police spokesman said yesterday evening.
First pictures from the tunnel yesterday showed cars and trucks not just burned-out, but in many cases fused together or melted beyond recognition.
"The shells of the cars had melted to the ground. Some of the victims we found on the tarmac were just a metre away from the emergency exits . . . they couldn't have known what was happening to them," one firefighter told Swiss newspaper Le Temps.
The 11 victims recovered so far were overcome by fumes from burning tyres, carried by one of the two trucks involved in the collision that led to Wednesday's fire.
Yesterday crews erected braces at one-metre intervals along the 17 km tunnel to support the roof, which engineers say was weakened by the intense heat and could collapse during the rescue effort.
As many as 40 vehicles could be trapped in "zone red", 1.5 km from the south entrance.
"There's a 50-metre stretch where there's a huge amount of wreckage and rubble which has all been fused together by the temperature of the fire," said Mr Romano Piazzini, Ticino canton police commissioner.
The Swiss government has rejected as unjustified calls for a second tunnel to be built at Gotthard, and another road tunnel, to separate traffic and increase safety.
"The risks bear no relation to the cost," according to Mr Michel Egger, vice-director of the Ministry for Roads.
He said that the Gotthard Tunnel, a key north-south axis through Switzerland, would "certainly remain closed until far into the winter".
The Swiss government is considering introducing legislation forcing goods transport onto the railways.
Le Temps said that after the collapse of national airline Swissair and the recent shooting of 14 people in a regional parliament, Switzerland was "searching for a meaning to it all".
