A suicide bomb attack on a classroom of hundreds of students preparing for exams in the Afghan capital on Friday killed at least 19 people, with most of the casualties girls, police and a witness said.

The blast ripped through Kaaj Higher Educational Center, which coaches mainly adult men and women ahead of university entrance tests.

"We were around 600 in the classroom. But most of the casualties are among the girls," Akbar, a student who was wounded in the attack, told AFP from a nearby hospital.

The bombing happened in the Dasht-e-Barchi neighbourhood of western Kabul, a predominantly Shiite Muslim area home to the minority Hazara community, the target of some of Afghanistan's most deadly attacks.

"Students were preparing for an exam when a suicide bomber struck at this educational centre. Unfortunately, 19 people have been martyred and 27 others wounded," Kabul police spokesman Khalid Zadran said.

A shopkeeper from the area said there was a loud explosion and then crowds of students rushed out of the centre.

"It was chaos as many students, boys and girls, tried to escape from the building. It was a horrific scene. Everyone was so scared," he told AFP anonymously.

Videos posted online and photos published by local media showed bloodied victims being carried away from the scene.

"Security teams have reached the site, the nature of the attack and the details of the casualties will be released later," Abdul Nafy Takor, the interior ministry's spokesman, earlier tweeted.

"Attacking civilian targets proves the enemy's inhuman cruelty and lack of moral standards."

- Scenes of chaos -
Families rushed to area hospitals where ambulances arrived with victims, and lists of those confirmed dead and wounded were posted on the walls.

"We didn't find her here," a distressed woman looking for her sister at one of the hospitals told AFP. "She was 19 years old."

"We are calling her but she's not responding."

Taliban members forced families of victims to leave the site of at least one hospital, fearing a follow-up attack on the crowd.

By Friday afternoon the Taliban allowed journalists to visit the educational centre.

The roof of the hall where students had gathered for a test had completely collapsed, while its doors and windows were blown out, an AFP correspondent reported.

Municipal workers were cleaning the floor, but still some patches of dried blood and pieces of flesh lay scattered.

- Frequently attacked neighbourhood -
The Taliban's return to power in Afghanistan last year brought an end to the two-decade war and a significant reduction in violence, but security has begun to deteriorate in recent months.

Afghanistan's Shiite Hazaras have faced persecution for decades, with the Taliban accused of abuses against the group when they first ruled from 1996 to 2001.

Such accusations picked up again after they swept back to power.

Hazaras are also the frequent target of attacks by the Taliban's enemy, the Islamic State (IS) armed group. Both consider them heretics.

Many attacks have devastated the Dasht-e-Barchi neighbourhood, with several targeting women, children and schools.

Last year, before the Taliban returned to power, at least 85 people -- mainly girl students -- were killed and about 300 wounded when three bombs exploded near their school in the area.

No group claimed responsibility, but a year earlier IS claimed a suicide attack on an educational centre in the same neighbourhood that killed 24, including students.

In May 2020, the group was blamed for a bloody gun attack on a maternity ward of a hospital in Dasht-e-Barchi that killed 25 people, including new mothers.

And in April this year, two deadly bomb blasts at separate education centres in the area killed six people and wounded at least 20 others.

Education is a flashpoint issue in Afghanistan, with the Taliban blocking many girls from returning to secondary education. The Islamic State also stands against the education of women and girls.