Search and rescue teams are working through the rubble of a building that collapsed in Plaka, the historic district beneath the Acropolis, after a powerful explosion on Friday morning, with five people still unaccounted for.

The blast tore through the building at 15 Lysikratous Street, near its junction with Amalias Avenue, at around 7.35am and was followed by a fire.

According to the Hellenic Fire Service, the missing are an elderly couple who lived on the second floor and three tourists, thought to be American, who had been staying in a short-term rental on the first floor. It is not yet known whether the tourists were inside when the explosion happened.

Firefighters, among them officers from EMAK, the fire service’s specialist disaster response unit, are searching the debris with thermal imaging cameras and a trained search dog. Drones are also being used to survey the site, while machinery supplied by the City of Athens is clearing away rubble.

Two women were freed from a neighbouring building during the rescue operation and taken by ambulance to Georgios Gennimatas General Hospital. A third person suffered minor injuries from flying debris.

Athens Mayor Haris Doukas, who went to the scene, described the situation as “very complex”. Asked whether anyone was trapped, he said: “There is great fear. There are missing people, and that is why search dogs are inside right now.”

“The explosion was extremely powerful and the destruction is extreme,” Doukas said. “These are critical moments that call for very good coordination.”

He said the city’s municipal police had sealed off the area from the outset, and that council engineers and civil protection staff would remain at the site to check the load-bearing capacity of adjoining buildings. Local media reported that a neighbouring building dating from 1880 may also be declared unsafe.

Asked about the cause, the mayor said he understood it had been a gas explosion. “Its intensity was terrifying, which means there was a very serious fault. Something went completely wrong,” he said.

The authorities are investigating whether a natural gas leak was to blame. Initial information suggests gas installations were located on the second floor.

Residents described the noise of the blast as deafening. It damaged nearby buildings and several parked cars, with at least eight vehicles reported to have been hit. Officers from the Hellenic Police and ambulances from the National Emergency Aid Centre (EKAB) are also at the scene.

The building had a basement, an unoccupied ground floor and two upper storeys. The first-floor flat was let through Airbnb, while the second floor was home to the missing couple. That has focused the search on the debris of the upper floor, where rescuers are moving with particular caution because the collapse has left the structure unstable.

Matthaios Artavanis, who owns the ground floor, said he learned of the explosion from the news and recognised his building in photographs. He immediately rang a neighbour for information.

“I was worried about the couple, who are friends. I called them at 8am but got no answer. The landline said there was a technical fault and the mobile was switched off,” he said. “It is a bleak situation. I haven’t been able to reach them, and from the photos I’ve seen, there is nothing left.” He added that the husband had limited mobility.

Andreas Martzakis, one of the co-owners of the Airbnb, said three guests had been registered under the name Frederick. “Did they get out or not? We have no idea since the explosion,” he said. “Nobody knows yet. We had three people on the first floor, and on the second floor there were two more, an elderly couple. The fire service hasn’t told us whether it has found anything.”

Martzakis said the rental had no natural gas supply and no propane or LPG cylinders. He lives about 50 metres away and was having coffee when he heard the blast. He ran outside and went to help a friend, Abdul, out of his car. Abdul was injured by broken glass, and the back of the vehicle was completely destroyed.