Casualties were feared as an explosion ripped through a busy road in western part of Afghan capital of Kabul on Wednesday, a witness said.

Afghan policemen stand guard at the site of an attack at American University of Afghanistan in Kabul, Afghanistan August 24, 2016.(Photo/Agency)

"A private college, American University of Afghanistan, could be the obvious target of the attack. A thick black smoke was rising near the gate of the college after the explosion which occurred roughly at 07:00 p.m. local time," witness Mohammad Salim told Xinhua.

The targeted building is located along the four-line Dar-ul-Amand road which leads to the parliament building.

"The blast caused panic among the residents. Security forces have cordoned off the area for precautionary measures. Several warning shots were also fired. The explosion also triggered a fire as I witnessed," Salim said.

"There is fear of possible causalities. So far, we have no more details, but we will try to get more information,"a security source told Xinhua near the site.

The nature of the blast looked like a suicide car bombing, he said.

Several ambulances and fire trucks were rushing to the site following the blast.

No group has claimed responsibility for the attack yet.