Militants stormed the city of Kunduz at dawn, battling to the city centre.
The city is a useful gain for the Taliban, as a hub for transportation in the north of the country. Its loss is a also substantial security breach for the government, the biggest such loss since 2001.
The assault occurred a day before the anniversary of President Ashraf Ghani’s unity government.
Video sent to Channel 4 News shows the group raising the white Taliban banner in the city centre, with the group now battling to take the airport.
The city was a stronghold of the Taliban prior to their overthrow in 2001. Hundreds of prisoners were said to have been freed.
Taliban spokesman Zabihullah Mujahid wrote on Twitter: “With the capturing of the police compound and governor’s office in Kunduz, the whole province fell to our hands and our fighters are now advancing towards the airport.”