Gunmen on motorcycles on Wednesday shot dead seven policemen guarding a polio vaccination team in Pakistan’s southern port city Karachi, officials said, a brazen attack in the country’s economic hub.

Gunmen on motorcycles on Wednesday shot dead seven policemen guarding a polio vaccination team in Pakistan's southern port city Karachi, officials said, a brazen attack in the country's economic hub.

Feroz Shah, a senior police official told AFP that eight gunmen carried out the killings in two separate attacks in the city's western Orangi Town neighborhood.

"The gunmen first opened fire on three policemen in the streets of Orangi Town, killing them all," he said, adding: "Later they shot dead four policemen, who were sitting in a police mobile van" a few streets away.

Abdul Kareem, an official in Abbasi Shaheed Hospital where the bodies were taken, also confirmed the casualties.

The polio workers, who were unharmed in the attack, were on the third day of an immunization drive.

Provincial home minister Sohail Anwar Siyal, told the private Dunya TV channel: "The policemen sacrificed their lives to protect the polio workers."

No group immediately came forward to claim responsibility, but Islamist outfits including the Pakistani Taliban say the polio vaccination drive is a front for espionage or a conspiracy to sterilize Muslims.

Pakistan is one of only two countries where polio, a crippling childhood disease, remains endemic.

Attempts to eradicate the disease have been badly hit by militant attacks on immunization teams that have claimed more than 100 lives since December 2012.