According to The Dawn, a team, comprising of the Pakistan Police, intelligence officials and a special protection unit (SPU), have launched a search operation to find the missing engineer - 36-year-old Pingzhi Liu.
Liu has been suspected of being swept away by the river.
However, the police are not denying a possibility of kidnapping as Liu's mobile phone was switched off.
The missing Chinese engineer had come to Islamabad last year to work on the power project, the police said.
He was last spotted by his colleagues while walking out of the tunnel on early Wednesday.
The police are investigating the matter and have questioned the five drivers, who were also working on the tunnel site with the Chinese engineer, but the drivers had no clue.
The Senior Superintendent of Police SPU Syed Ali Mohsin said more than 300 Chinese were working on the power project and an advisory to follow standard operating procedure regarding security at their workplace and residence had been issued. (ANI)