Passengers trapped in the Salang pass, the main route across the Hindu Kush mountains, said by telephone that they were freezing to death and being suffocated by car fumes, and had seen cars filled with dead bodies after being stuck through the night.
A force of 600 soldiers plus police units and other emergency workers had managed to evacuate 1,500 trapped people, including at least 70 who were injured, the Defence Ministry said in a statement that gave a death toll of 28.
Days of heavy snow triggered avalanches blocking the 2.6 km (1.6 mile) long Soviet-built tunnel, a historic engineering feat that links Kabul and Afghanistan's north, connecting the Indian subcontinent to Central Asia through the treacherous mountain pass at 3,400 metres (11,000 feet).
I saw five dead bodies from a car parked behind us, and so far the government has not done enough to save our lives, Qazi Azhar, an Afghan judge who was caught in the pass, told Reuters by mobile phone.
Another passenger, Ghulam Yahya, said passengers inside the tunnel were suffering from fumes.
Many others will die if we don't get help on time, he said.
President Hamid Karzai said he was saddened by the deaths and ordered government workers to do all possible to open the pass.
Abdul Mateen Edraak, head of Afghanistan's National Disaster and Preparedness Centre, said fears were greatest for passengers stuck in cars exposed to the extreme cold.Some 50 cars which are exposed to extreme weather are a concern for us but others inside tunnel are not bad, he said. The people are stuck there for more than 24 hours and if there are no other avalanches we will hopefully bring them out by end of the day.
Edraak said there had been 17 avalanches reported so far and more than 200 trucks, buses and cars were trapped inside the tunnel, which made the rescue operation more difficult.
Heavy snowfall and rain also caused floods in the south of the country. Zalmay Ayoubi, spokesman for the governor of southern Kandahar Province, said six people had been killed and 10 were missing as a result of floods.
(Reporting and Writing by Hamid Shalizi; Editing by Nick Macfie and Alex Richardson)