People speak on their phones as they stand outside their office after a strong quake hit Athens on Friday. Petros Giannakouris / AP

• The fire department rescues over a dozen of people trapped in elevators in the capital
• The government denies ordering an evacuation alert
• News media reported electricity outages but said internet connections were still operating

A magnitude 5.1 earthquake shook the Greek capital Athens on Friday, sending people running from buildings in panic, witnesses said.

Quake knocked out phone and cellphone service and sent worried residents rushing into the streets, but there were no immediate reports of damage or injuries.

According to the Greek geodynamic institute, it was a 5.1-magnitude quake with an epicentre 23 kilometres orthwest of Athens and was followed by aftershocks.

The quake struck at around 1100 GMT at a depth of 13 kilometres, news reports said.

No evacuation alert

Worried residents and office staff have crowded outdoor areas but the government denied it had ordered an evacuation alert.

The fire department rescued over a dozen people trapped in elevators in the capital, state broadcaster ERT said.

"People must remain calm," said Efthymios Lekkas, head of the state anti-quake protection agency.

"There is no reason for concern. The capital's buildings are build to withstand a much stronger earthquake," he told ERT.

The epicentre was near the area where a 5.9-magnitude quake left 143 people dead in and near Athens in 1999.

The US geological institute said Friday's quake had a magnitude of 5.3.

Aftershocks

"For the time being we cannot be sure whether this was the main earthquake," seismologist Gerassimos Papadopoulos told ERT.

"There have been at least three (smaller) aftershocks already, which is a positive sign," he said, adding that the quake was felt as far as the Peloponnese islands.

"People in the capital must remain calm... they must be psychologically ready for more aftershocks," he said.

News media reported electricity outages but said internet connections were still operating.

Greece lies on major fault lines and is regularly hit by earthquakes, but they rarely cause casualties.

In July 2017, a 6.7-magnitude earthquake killed two people on the island of Kos in the Aegean sea, causing significant damage.

Agence France-Presse