At least 43 people were killed and 13 wounded when gunmen opened fire on their bus in Karachi Wednesday, Pakistani police said, in the second deadliest attack on the minority sect this year.

At least 43 people were killed and 13 wounded when gunmen opened fire on their bus in Karachi Wednesday, Pakistani police said, in the second deadliest attack on the minority sect this year.

"According to the initial information which we have received from hospitals, 43 people have been killed and 13 wounded," Ghulam Haider Jamali, police chief of Sindh province told reporters at the site.

"Six terrorists came on three motorcycles, they entered the bus and began firing indiscriminately. They used 9mm pistols and all those killed and injured were hit by the 9mm pistols," he said.

Television images from the scene showed a large pink bus that had been stained by blood in some parts, while anxious relatives rushed to visit the wounded in nearby hospitals.

ISIL group on Wednesday claimed responsibility for the attack, according to AFP.

It was the worst attack since January 30, when a suicide bomber blew himself up in a mosque in the southern Shikarpur district, killing 61.

Terrorists have increased attacks in recent years in Karachi and also in the southwestern city of Quetta, the northwestern area of Parachinar and the far northeastern town of Gilgit.