Unidentified gunmen on Monday fired multiple shots at two Chinese nationals and injured one of them critically in a targeted attack in a upmarket area of Pakistan's southern city of Karachi, police said.

The two Chinese were in their car in the Zamzama district when the attackers in another car opened fire on their vehicle.

One of the Chinese suffered two bullet wounds to his head and the other was shot in the leg, senior police officer Azad Khan told AFP.

"Apparently it seems to be a targeted attack," Khan added. Police collected nine bullet casings.

A Pakistani passer-by suffered minor injuries.

A hospital official said the Chinese who was hit in the head was very seriously hurt.

"We are trying our best to save his life but his condition is highly critical," doctor Seemi Jamali, the head of the government hospital where he was brought, told AFP.

The two Chinese were working for a shipping company. One of them was identified as Chen Zhu, aged 46, police said.

Thousands of Chinese engineers and technicians are working in Pakistan.

China is ramping up investment as part of a $54 billion project known as the China-Pakistan Economic Corridor, upgrading infrastructure, power and transport links between its far-western Xinjiang region and Pakistan's Gwadar port.

Last October Pakistan confirmed the death of two Chinese nationals who were kidnapped in the southwestern city of Quetta, months after the Islamic State group claimed it had killed them.

The pair, a man and a woman, had been dragged into a car in May 2017 by three men, witnesses said, adding that another Chinese woman managed to escape.