ISLAMABAD, Nov. 23 (Xinhua) -- At least 6 people were killed and 20 others injured when a bomb went off in Pakistan's northwest tribal region of Orakzai Agency on Friday, local media reported.

According to reports, the blast happened at the main gate of a seminary in the lower part of Orakzai Agency, one of Pakistan's seven mountainous tribal regions located near the Pakistan-Afghan border.

Following the explosion, rescue teams along with security forces have rushed to the blast site and the injured people have been shifted to the nearest hospital.

Several among the injured people were in critical condition, said the hospital sources.

Security personnel cordoned off the area after the blast and launched a search operation.

The nature of the blast is not known yet, and police have launched an investigation into the incident.

No group or individual has claimed the attack yet.