Up to four gunmen tried to enter the consulate but were intercepted by security guards at a checkpoint, senior local police official Javaid Alam Odho told AFP.

An exchange of fire resulted "killing two of our constables and critically wounding another", he said.

He added that the attackers "ran away" but did not confirm if the attack was over, saying the area had been cordoned off and security forces were conducting a clearing operation. 

"Police and Rangers have reached the site," added senior police official Pir Muhammad Shah.

Pictures posted to social media purportedly of the attack showed smoke rising from the area.

Karachi, Pakistan's largest city and a financial hub, was for years rife with political, sectarian and ethnic militancy.

A crackdown in the city by security forces in recent years has brought a lull in violence, but scattered attacks still take place.

China, one of Pakistan's closest allies, has poured billions into the South Asian country in recent years as part of a massive infrastructure project that seeks to connect its western province Xinjiang with the Arabian Sea.

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