A Chinese contractor has resumed construction on a major dam site in northwestern Pakistan after being provided with extra security, officials said on Wednesday, following a deadly attack on Chinese engineers.

Power China and the China Gezhouba Group Company had halted work on a pair of dam projects last month in Khyber Pakhtunkhwa province after a suicide bomber killed five Chinese nationals and a Pakistani driver, causing their van to plunge into a deep ravine.

Hundreds of Chinese people are employed at the Dasu and Diamer Bhasha dam construction sites, located around 100 kilometres apart in the mountainous region.

Power China resumed work on the Diamer Bhasha dam on Monday after security was "significantly increased", Nazakat Hussain, a spokesman for the project, said.

Pakistani police have detained more than 12 people, including Afghan nationals, in connection with the bombing.

Prime Minister Shehbaz Sharif visited Chinese workers earlier this week, vowing to put in place "foolproof" security arrangements and promising "exemplary punishment" of attackers. (AFP)