No militant group immediately claimed responsibility for the rare attack on Japanese nationals, however, with Pakistani authorities identifying them as engineers working for the management of an export processing zone in the port city.

Five Japanese nationals in Pakistan escaped unhurt on Friday from a suicide bomb attack on their vehicle as police shot down a gunman accompanying the bomber, a police spokesperson said, but two bystanders were among the three injured.

Islamist militants seeking to overthrow the government and set up their own strict brand of Islamic rule have launched some of Pakistan's bloodiest attacks during the last few years, with some separatist groups targeting foreigners, including Chinese.

No militant group immediately claimed responsibility for the rare attack on Japanese nationals, however, with Pakistani authorities identifying them as engineers working for the management of an export processing zone in the port city.

The Japanese have been moved to a safe place in police custody, the spokesperson, Abrar Hussain Baloch, said, although the bystanders and a guard with the visitors suffered injuries.

One of the two motorcycle-borne attackers set off explosives tied to his body as soon as the vehicle slowed, Pakistani counter-terrorism official Raja Umar Khatab told reporters, but failed to strike his target.

That prompted his accomplice to start shooting at the vehicle.

"I think he fired some 15 or 16 shots," Khatab said, adding that private security guards with the foreigners and a nearby police patrol returned fire and killed the second attacker.

The men had followed the Japanese group's vehicle for some time before the attack, he said, with authorities suspecting they carried out reconnaissance to identify the target and location of the attack.

Prime Minister Shehbaz Sharif condemned the attack, praising the timely police action for saving lives.