A massive blast on a road near the airport of Pakistan's largest city killed two Chinese nationals, Beijing's embassy said Monday, after a separatist militant group claimed an attack in the area.

An AFP journalist heard the explosion in Pakistan's southern megacity of Karachi around 11:00 pm (1800 GMT) Sunday.

The regional government of southern Sindh province said on X that a "tanker" had exploded on the airport motorway.

Separatist militant group the Baloch Liberation Army (BLA) said in a statement that it had "targeted a high-level convoy of Chinese engineers and investors" coming from Karachi's airport.

Beijing's embassy to Pakistan said in a statement on Monday that two Chinese citizens had been killed in a "terror attack" on a convoy of personnel from the Chinese-funded Port Qasim power project.

The attack also left one Chinese and several Pakistani citizens wounded, the embassy said.

The embassy urged authorities to "conduct a thorough investigation of the attack and severely punish the killers, while at the same time taking practical measures to fully ensure the safety of Chinese citizens, institutions and projects".

The BLA is a separatist militant group advocating for autonomy of Pakistan's Balochistan province, the largest but poorest region of the country.

The group has regularly targeted Chinese nationals, claiming ethnic Baloch locals are not receiving their fair share of wealth extracted by foreign investors.

Pakistan's Civil Aviation Authority said flights from Karachi were continuing "as usual" and "agencies are investigating the cause at the scene of the accident/explosion".