Images on local news channels showed a damaged van, as police officers arrived at the scene of the incident. Awan said the three passersby who were wounded in the attack were in stable condition at a hospital.
Police were escorting the van after receiving reports about possible attacks on foreigners who are working in Pakistan on various Chinese-funded and other projects, said Tariq Mastoi, a senior police officer. He said a timely and quick response from the guards and police foiled the attack and both attackers were killed.
No one immediately claimed responsibility, but suspicion is likely to fall on a small separatist group or Pakistani Taliban who have stepped up attacks on security forces in recent years. Insurgents have also targeted Chinese who are working in Pakistan on projects relating to the China-Pakistan Economic Corridor, which includes a multitude of megaprojects such as road construction, power plants and agriculture.
In March, five Chinese and their Pakistani driver were killed when a suicide bomber in northwest Pakistan rammed his explosive-laden car into a vehicle when they were heading to the Dasu Dam, the biggest hydropower project in Pakistan, where they worked.
However, Japanese working in Pakistan have not been a target of any such attacks.
Karachi is the largest city of Pakistan and the capital of southern Sindh province.