Gunmen attacked a hotel in Pakistan's southwestern port city of Gwadar on May 11 and were battling security forces while helicopters circled overhead, officials said.
One official, who spoke on condition of anonymity because he was not authorised to talk to the media, told Reuters most guests had been evacuated from the five-star Pearl Continental Hotel but attackers appeared to have reached the first floor.
Gwadar, which lies on the Arabian Sea, is a strategic port being developed as part of the $60 billion China Pakistan Economic Corridor, which is part of China's mammoth Belt and Road infrastructure project.
Balochistan Home Minister Ziaullah Langove said there appeared to be casualties but there were no immediate details.
There was no immediate claim of responsibility.