2 American tourists dead after building explosion in Greece

An American couple in Greece died after a building collapsed, following an explosion on Friday, officials said.

Four other people were missing, including an elderly British man and a Greek woman who shared an apartment, after the explosion in Athens' historic Plaka district, below the Acropolis monument.

The American man and woman had been staying in an apartment rented to tourists located on the floor above street level, Greek rescue officials told journalists. Their identities were not immediately made public.

A rescue operation was ongoing, with according the Agence France-Presse news agency, who saw mechanical diggers moving debris and thermal-imaging cameras being deployed.

The explosion that brought down the small, two-storey building was likely caused by a gas leak, the mayor of Athens, Haris Doukas, said.

"We are talking about an incredible disaster," he said, adding that damage had occurred along the street the building was in, as well as behind it.

Doukas said that two nearby buildings were left in a dangerous state, with inspections under way "to determine if they can remain standing or if they also have to be demolished".

Some 30 rescuers and three sniffer dogs were at work at the site of the incident, Greece's ANA news agency reported.

A year ago, locals in the Plaka neighbourhood had warned the city and utility companies about the risk of gas leaks or short circuits, according to a letter by the residents' association published by the Kathimerini newspaper.

The residents had urged a fire drill to identify possible weaknesses in the emergency response plans for the district.

The neighbourhood is one of Athens's most popular tourist areas. The nearby Acropolis, one of Greece's best-known landmarks, welcomed 4.6 million visitors last year.