Rescue teams in Athens are searching for an elderly couple who lived on the top floor of a building in the historic Plaka district that collapsed after a powerful explosion on Friday morning.

Relatives and the authorities have repeatedly tried to reach the pair by phone without success. Their mobile appears to be switched off.

Investigators are trying to establish whether the couple were at home when the blast struck or had left earlier. Their presence on the second floor was known within hours of the incident, but there is still no confirmed information on their whereabouts.

Firefighters and officers from EMAK, the fire service’s special disaster response unit, are combing the debris with trained search dogs and specialist equipment.

The building at 15 Lysikratous Street had a ground floor and two upper storeys. The ground floor was unoccupied, while the first-floor flat was let as a short-term rental through Airbnb. The missing couple’s home was on the second floor.

That has focused the search on the rubble of the upper floor, where rescuers are working with particular care because the collapse has left the structure unstable.

Andreas Martzakis, one of the co-owners of the Airbnb, said three guests had been registered under the name Frederick. “Did they get out? Did they not? We have no picture since the explosion,” he said. “I was there from the very first moment. It’s the Airbnb that came down.”

Asked whether anyone had been inside, he said: “Nobody knows yet. We had three people on the first floor, and on the second floor there were another two, an elderly couple. The fire service hasn’t told us whether it has found anything inside.”

Martzakis said the property had no natural gas supply, propane cylinders or bottled gas. “I live 50 metres away, right here,” he said. “I was having a coffee and as soon as I heard it I went straight outside.” He said he saw his friend Abdul in a car and went to pull him out. Abdul was injured by broken glass, and the back of the car was completely destroyed.

The explosion happened shortly after 7.30am in an old building near the junction of Lysikratous Street and Vasilissis Amalias Avenue, opposite the columns of the Temple of Olympian Zeus.

The shockwave caused extensive damage to the building itself as well as to neighbouring homes, shops and parked cars. Windows shattered in nearby buildings and debris was thrown into the street.

Footage obtained by Proto Thema shows guests at a nearby hotel sitting in the breakfast room. Just after 7.34am a loud bang is heard, the windows shatter and guests run in panic towards reception.

The hotel’s owner said the tourists were terrified because they thought a bomb had gone off. One couple left their room for fear of a second explosion.

A passer-by suffered minor injuries, and two women were freed from a neighbouring building and taken for first aid.

The authorities are investigating the cause, and early indications point to a possible gas leak, with the fire service’s investigation unit examining the site. Residents and people working in the area said there had been a strong smell of gas before the blast, although the exact cause has yet to be established.

The priority remains finding the couple and confirming whether they were in their second-floor flat when the explosion happened.