Suspected militants on Friday gunned down three Pakistani workers building a Chinese-funded "Silk Road" highway in the country's southwest, just days after a similar attack killed 10, officials said.

There was no immediate claim of responsibility, but previous attacks in Balochistan have been unleashed by separatists who fear the construction projects are a ruse to take over their land.

Last week's attacks were claimed by the separatist Baloch Liberation Army (BLA).

The men killed on Friday were part of a team working on a major highway linking the port-city of Gwadar to the provincial capital of Quetta, said Sarmad Saleem, a regional official.

"One labourer died on the spot and two others succumbed to their injuries in hospital," Saleem said.

They were making a trip to a marketplace in the small town of Hoshab, 280km (174 miles) from Gwadar, to buy daily supplies, an official of the paramilitary force overseeing security in Balochistan, told Reuters.

Gwadar's deep-water port is the exit point for a planned route from China's far western region of Xinjiang to the Arabian Sea and is expected to start functioning by June 2018, an adviser to Prime Minister Nawaz Sharif told Reuters this month.

Pakistan expects up to four per cent of global trade to pass through it by 2020, he added.

For decades, Balochistan, where police jurisdiction is limited to major urban centres, has grappled with a campaign waged by separatist militants against the central government to demand a greater share of the gas-rich region's resources.

Militants have killed at least 54 Pakistani workers there since 2014, security officials say.

In 2015, Pakistan created an army division, estimated to number more than 10,000 troops, to protect projects and workers involved in its effort to upgrade infrastructure, for which China has pledged $57 billion in investments.

Known as the China-Pakistan Economic Corridor, it is part of a vast modern-day "Silk Road" network of trade routes linking Asia with Europe and Africa.