Armed men in Pakistan have killed the headmaster of a Karachi school and injured at least six people, including four school girls and two teachers.

Saturday's shooting in the port city of Karachi was carried out by two attackers. Authorities have yet to declare a motive.

Witnesses said the men on a motorcycle hurled a hand grenade at the building before running into the school, throwing another grenade and opening fire.

"We have found 3-4 shells of a 30. bore gun. As a result, Rasheed [school principal] has expired, and four

or five children are injured," a police official at the attack site said.

The four injured girls were brought to a nearby hospital.

An injured grade two student explained that students had been waiting to hear their examination results.

"The examination results were going to be announced. Two men came on a motorbike," Ameena said.

"Five were injured and one died. I don't know what else happened," she said.

The school's principal, Abdur Rasheed died while being moved to the hospital.

"After 15 minutes, suddenly a man ran in firing. We were all engrossed in the magic show. But as soon as the firing started, there was a stampede. I think they lobbed two hand grenades also," Attaur Rehman, a teacher injured in the attack, said.

No one has claimed responsibility for this attack so far.

Mir Hazar Khan Khoso, Pakistasn's careaker prime minister, condemned the attack, and directed local administration to provide all possible assistance to the affected families, a statement from his office said.