Pakistan ramped up security guarding Chinese engineers building Beijing-linked projects in the nation's northwest, an official said Wednesday, a day after five workers were killed in a suicide bombing.

Beijing is Islamabad's closest regional ally and Pakistan has benefitted from billions of dollars of investment in recent years, but has struggled to guarantee the safety of Chinese migrant workers.

The five Chinese engineers -- plus their Pakistani driver -- were killed while travelling between Islamabad and a hydroelectric dam construction site in Dasu, in northwestern Khyber Pakhtunkhwa province.

A high-ranking official from the provincial interior ministry told AFP on Wednesday that at the more than two-dozen sites hosting Chinese engineers in Khyber Pakhtunkhwa security was stepped up.

"Directives have been issued to all law enforcement agencies to enhance security for Chinese nationals and all other foreigners," he said on condition of anonymity.

"Instructions have also been given to foreign nationals to restrict their movements."

Information minister Attaullah Tarar told a press conference in Islamabad that security procedures would be reviewed "with a focus on identifying and addressing any gaps".

Meanwhile, further details emerged about the attack, which has yet to be claimed by any militant group.

Local police officer Bakht Zahir said the five engineers killed near the city of Besham included four men and a woman, and that the bomber targeted the middle vehicle in a convoy of 12.

"The suicide bomber rammed his vehicle into the convoy in the middle, detonating himself, causing the Chinese engineers' vehicle to fall into a 180-foot-deep (55-metre) ravine and catch fire," he said.

Pakistan's domestic chapter of the Taliban is the most active militant threat in the region, but the group's spokesman denied involvement in a statement late Tuesday.

China has inked more than two trillion dollars in contracts around the world under its Belt and Road investment scheme, with billions pouring into neighbouring Pakistan and aiding its crumbling economy.

Since 2015, power plants, ports and transport projects have been under construction by joint Pakistani-Chinese teams in remote parts of the South Asian nation.

But Chinese workers have frequently been targeted by militants hostile to outside influence, with some complaining Pakistanis are not getting a fair share of wealth from the huge projects.

Tuesday's attack came just days after militants attempted to storm offices of the Gwadar deepwater port in the southwest, considered a cornerstone of Chinese investment in Pakistan.

It sparked a flurry of diplomatic activity at the Chinese embassy in Islamabad, with Prime Minister Shehbaz Sharif and the foreign and interior ministers offering condolences in quick succession.

China's foreign ministry declared the countries "iron-clad friends" but asked Pakistan to "take effective measures to ensure the safety and security of Chinese nationals, projects, and institutions".