The labourers, working on a bridge at Sohrab Dam in Gagdan area of Turbat, were sleeping in their camp when gunmen attacked them, police officer Imran Qureshi said.
The militants came on motorbikes and opened indiscriminate fire on labourers around 2 AM, he said.
Qureshi said that 16 of the dead belonged to Punjab while four hailed from Sindh province.
Three workers were injured in the attack. The injured were rushed to District Headquarter Hospital.
Nationalists also blame Punjabi dominated security forces as responsible for highhandedness in the province, an allegation denied by the armed forces and federal government.
Balochistan Chief Minister Abdul Malik Baloch arrived in Turbat to chair a high-level meeting on the incident and concerns regarding security.
It is also the home town of the Chief Minister.
