At least six people were killed after a building collapsed in Gurugram early on Thursday, ANI reported. The incident took place in Ullawas village.

The operation to rescue those trapped is still under way. Three teams of the National Disaster Response Force and State Disaster Response Force are part of the rescue operation.

Gurugram’s Chief Fire Officer IS Kashyap said three victims had been identified, IANS reported. “The deceased were security guards hailing from nearby states and were working here,” he said.

The sub-divisional magistrate of Gurugram, Sanjeev Singla, told ANI that the four-storey building was unstable and being built “without any technical expertise”. The exact number of people trapped is unknown, he said.

Gurugram Deputy Commissioner Vinay Pratap Singh told ANI that the cause of the collapse is still unknown, but that the building owner, identified as Dayaram, has been found.

Gurugram Police spokesperson Subhash Boken told reporters that the building’s fourth floor was completed on Wednesday, The Hindu reported.

Resident living near the building claimed it was constructed without permission, the Hindustan Times reported.

Rescue workers at the site of building collapse in Gurugram on Thursday.