KABUL, May 8 (Xinhua) -- Several people were either killed or injured after a big explosion and ensuing gunfire rocked an aid agency in the central part of Afghanistan's capital of Kabul, causing panic among residents on Wednesday, the government said.

"The blast occurred outside an aid agency in Police District 10. The Crisis Response Unit (CRU) has arrived at the site and is battling with the terrorists at the site," Afghan Ministry of Interior Affairs said in a statement.

Further details will be released later in the day, the statement added.

"We heard a huge blast in Shahr-e-Naw locality roughly at 11:40 a.m. local time. The whole place has now been sealed off by CRU or elite police forces," eye-witness Aman Karimi told Xinhua earlier.

The incident caused casualties and destruction in the business district where scores of offices and shops are located.

The blast caused a plume of grey smoke to rise above the scene, he said.

Rescue teams, police and security forces rushed to the area, waiting for access to the site of the attack.

No group has claimed the incident so far.