Taliban fighters have captured Mazar-e-Sharif, the last major city in northern Afghanistan which was still under government control.
The fall of the traditional anti-Taliban bastion marked a major gain for the militants, who have been advancing at speed as US-led forces withdraw.
President Ashraf Ghani travelled to the city just days ago to rally troops.
The Taliban are now in control of much of the country and are edging closer to the capital Kabul.
More than a quarter of a million people have been displaced by the violence, and many have headed to Kabul in hopes of finding safety.
Women in areas captured by the Taliban have described being forced to wear burkas and the militants are also reported to have beaten and lashed people for breaking social rules.
Local officials said Mazar-e-Sharif – the fourth largest city in Afghanistan – fell largely without a fight.
Abas Ebrahimzada, a lawmaker from Balkh province whose capital city is Mazar-e-Sharif, told the Associated Press news agency that the national army were the first to surrender, which then prompted pro-government forces and other militia to give up.
Mazar-e-Sharif is a major economic centre that lies close to the borders with Uzbekistan and Tajikistan. The last time the Taliban took the city was in the 1990s.
Ethnic Uzbek warlord Abdul Rashid Dostum and prominent ethnic Tajik leader Atta Mohammad Noor are reported to have fled the province. Details of their whereabouts are unknown.
Following crisis talks with Mr Ghani earlier this week, Mr Dostum struck a defiant tone, saying: “The Taliban have come to the north several times but they were always trapped.”
Other areas also fell to the Taliban on Saturday, including the capitals of Paktika and Kunar provinces.
Unverified footage from the city of Asadabad, in Kunar, showed people waving the Taliban flag and walking through the streets.
The Taliban are now in control of more than half of the provincial capitals in the country. The only major cities to remain under government control are Kabul and Jalalabad.
Is the Afghan government doing anything to stop the Taliban?
In a pre-recorded TV address earlier on Saturday, Mr Ghani said a top priority was the remobilisation of the Afghan armed forces to prevent further destruction and displacement of people.
Mr Ghani said he would not let a war that was “imposed” on people “cause more deaths”, and praised the “courageous” security forces.
The speech came amid speculation by some that Mr Ghani may have been about to announce his resignation.
The UN has appealed to neighbouring countries to keep their borders open so that displaced Afghans can reach safety. UN Secretary General António Guterres said the situation was spinning out of control.
The US is preparing to airlift thousands of people a day out of the capital.
Some 600 British troops are due to arrive in the city this weekend to help with the withdrawal of UK citizens. They will also assist the relocation of Afghans who helped British forces and now risk reprisals from the Taliban.
Other Western countries are also evacuating their nationals, scaling back their presence in Afghanistan and in some cases closing their embassies altogether.