Kabul, Afghanistan (CNN) The Taliban have captured a district in northern Afghanistan, police tell CNN, reportedly forcing thousands of people to flee.

After almost two days of heavy clashes, Afghan security forces withdrew Saturday from Qala-e-Zal district, one of six within Kunduz province, according to Mahfuzullah Akbari, a regional police spokesperson.

An Afghan National Army commando aims his weapon amid ongoing fighting between Taliban militants and Afghan security forces in Kunduz on October 5, 2016.

Clashes continue between Afghan security forces and the Taliban on the Kunduz-Khanabad highway, where Afghan troops are trying to clear the road for local residents, he added.

Afghanistan has been in a fight to hold off the Taliban in Kunduz province since the insurgents briefly captured the city of Kunduz in September 2015 and October 2016.

Residents forced to flee

After Saturday's developments in Kunduz, hundreds of families were "desperately fleeing," said Kate O'Rourke, Norwegian Refugee Council (NRC) country director in Afghanistan. "Many are accommodated with extended families elsewhere, but some have had to sleep in the open."

The Qala-e-Zal district is one of six within the northern province of Kunduz.

Rahman Gerdi, 29, a civilian from Aq Tapa, told NRC emergency response staff in Kunduz about his experience.

"Taliban fighters were shooting from one side of our house and the Afghan National Security Forces (ANSF) from the other side," Gerdi said. "A rocket landed in my garden. My wife told me that if I didn't flee, she would leave the house alone with our two daughters. We fled. We left everything behind. I'm afraid it will be looted."

Preliminary reports from local authorities and aid groups indicate that thousands of people have been displaced.

'We were all afraid'

Abdul Karim, 31, from Qala-e Zal, fled with his family to Kunduz city, where he is staying in a compound with four other families.

Residents flee Kunduz in October 2015.

"Around 2:30 a.m. Taliban fighters came to our houses and asked us to evacuate. They told us not to make any sound. We were all afraid," he told the NRC on Saturday.

Juma Khan Hakimi, 75, a resident of Qala-e-Zal, told CNN that after taking the district, Taliban forces destroyed all police checkposts.

He said people were forced to leave their belongings in their homes and live under tents in the desert. The Taliban cut off water.

"The government does not have a proper attention on our district. That is why the district falls for the third time," he said. "One week before we knew that Qala-e-Zal would fall we told government officials about it, but they did not pay attention."

Annual spring offensive

The escalation in fighting follows the Taliban's announcement last week of their annual spring offensive.

Last month, Taliban fighters disguised in Afghan military uniforms killed an estimated 140 people in an attack on a military base mosque and dining facility.

A wounded Afghan National Army soldier lies on a hospital bed after last month's Taliban attack.

US troops have been fighting in Afghanistan for almost 16 years against the resilient Taliban. About 8,400 US troops and 6,000 troops from allied countries remain in Afghanistan.

In February, Gen. John Nicholson, commander of US forces in Afghanistan, called the situation "a stalemate."

Last week, military officials said the Pentagon might send more troops to Afghanistan to get past it.