A suicide bomb attack on worshippers at a Shiite mosque in the Afghan city of Kunduz killed at least 55 people Friday, in the bloodiest assault since US forces left the country.

Scores more victims from the minority community were wounded in the blast, which has not been claimed but appears designed to further destabilise Afghanistan in the wake of the Taliban takeover.

Taliban spokesman Zabihullah Mujahid had earlier said an unknown number of people had been killed and injured when "an explosion took place in a mosque of our Shiite compatriots" in Kunduz.

There was no immediate claim of responsibility for the attack, but the Islamic State group, bitter rivals of the Taliban, has claimed similar recent atrocities. 

Residents of Kunduz, the capital of a province of the same name, told AFP the blast hit a Shiite mosque during Friday prayers, the most important of the week for Muslims.

Zalmai Alokzai, a local businessman who rushed to Kunduz Provincial Hospital to check whether doctors needed blood donations, described horrific scenes. 

"I saw more than 40 dead bodies," he told AFP. "Ambulances were going back to the incident scene to carry the dead." 

An international aid worker at the MSF hospital in the city told AFP there were fears the death toll could rise. 

"Hundreds of people are gathered at the main gate of the hospital and crying for their relatives but armed Taliban guys are trying to prevent gatherings in case another explosion is planned," he said.

- Frightened crowds -
Graphic images shared on social media, which could not immediately be verified, showed several bloodied bodies lying on the floor. 

Another video showed men shepherding people, including women and children, away from the scene. Frightened crowds thronged the streets.

Kunduz's location makes it a key transit point for economic and trade exchanges with Tajikistan. 

It was the scene of fierce battles as the Taliban fought their way back into power this year.

Often targeted by Sunni extremists, Shiite Muslims have suffered some of Afghanistan's most violent assaults, with rallies bombed, hospitals targeted and commuters ambushed.

Shiites make up roughly 20 percent of the Afghan population. Many of them are Hazara, an ethnic group that has been heavily persecuted in Afghanistan for decades.