TBILISI, DFWatch–Four people died when a building collapsed in central Tbilisi on Monday.

Three of them died on the spot, while the fourth, believed to be 17 or 18 years old, died of his injuries at the hospital.

The three dead were laborers working to demolish a building in Saburtalo, behind Sports Palace, in downtown Tbilisi, while the fourth, the teen, was a relative of the workers who accidentally visited the site during the collapse.

The building was erected during Soviet times and was used by the Institute of Mathematics, but was recently sold to Tiflis Business Center, and refurbishing is ongoing with plans to open a hotel there.

All four victims were from the same family, according to the media accounts.

It is still not known what caused the collapse. The Ministry of Internal Affairs has already launched a criminal investigation into the case on the grounds of possible violations of the safety rules.