Rescuers found one person dead under the rubble of a house in Medan's Grand Polonia complex early Tuesday, more than 12 hours after an explosion leveled the building. A joint search and rescue team is still looking for two others believed trapped inside.

The blast tore through House No. 3B in the Medan Polonia subdistrict around 3:30 p.m. on Monday, damaging six to seven nearby buildings and several vehicles hit by flying debris.

Hery Marantika, head of the Medan Class A Search and Rescue Office, said the victim found overnight was evacuated immediately. "The joint SAR team is continuing an intensive search, using methods adapted to the condition of the rubble. At 2:20 a.m. this morning, one victim was found dead and immediately taken to Bhayangkara Hospital," he said in a statement released at 8:29 a.m.

Why is the cause of the blast still unconfirmed?

Two official sources have reported different stages of the investigation. Medan Police Chief Kombes Pol Jean Calvijn Simanjuntak said the initial probe points to a leak in an underground gas pipe, while PGN, the state gas utility, said it detected no methane when it inspected the site after the explosion. A final determination is still pending checks of the physical condition of the pipe and where the damage started.

"The initial investigation points to a leak from a buried or underground gas pipe," Simanjuntak said. Agus Kurniawan, PGN's area head for Medan, gave a different reading from his team's measurements. "Checks at the site, including on the first and second floors of the affected house, showed a reading of 0 ppm, meaning no methane was detected," he said. Ppm, or parts per million, is the unit gas detectors use to measure methane concentration in the air; a zero reading means the device picked up no gas when it was run.

That zero-ppm reading came after the explosion, once PGN had already shut off gas supply to the area, so it reflects conditions after the blast rather than the state of the pipe beforehand. PGN has sent technical and emergency response teams to the site to inspect the network further.

Seven people in the house, two still missing

Police said seven people were inside the house when it exploded. Four of them, including a toddler, were evacuated safely first; the toddler was taken to hospital. The remaining three were trapped under the rubble. As of Tuesday morning, one had been found dead and two were still being searched for.

Wiwin, a construction worker who was resting next door with five colleagues, saw a flash of light just before the blast. He and his colleagues were hit by flying glass and ran from the building. The explosion happened during heavy rain and strong wind.

Brimob deploys bomb squad and SAR team

The damage spreading to surrounding homes prompted North Sumatra Police's Mobile Brigade (Brimob) to send in three specialized units at once. "We deployed dozens of personnel from the Bomb Disposal Team and the CBRN team from the Gegana Detachment, along with the SAR Team from the A Pelopor Battalion, to support the response at the explosion site," said M. Rendra Salipu, commander of Brimob North Sumatra. The bomb disposal team is checking the rubble for possible explosives, while the CBRN team is screening the area for hazardous substances.

The search for the two remaining victims continues with heavy equipment, adjusted carefully to the rubble's stability. Investigators are examining the condition of the underground pipes, gas network pressure records from before and after 3:30 p.m. Monday, and any other possible ignition sources near the house. PGN has not said when gas service in the area will resume.