A powerful 6.4-magnitude earthquake struck the western Greek island of Zakynthos early Friday, causing slight damage to the port and some buildings but no one was injured, authorities said.

The quake, which was felt as a tremor as far away as Italy, Albania and Malta, caused rocks to tumble down the island's slopes, in some cases crashing into beaches, and led several of the island's 40,000 residents to spend the night out on the streets, authorities said.

"Kudos. Building regulations work in seismic zones. Earthquake-resistant buildings on Greek island Zakynthos survive 6.4 earthquake: no injuries reported," said the United Nations office for disaster and risk reduction.

However, and a 15th-century monastery on the nearby islands of Strofades endured some damage, a Zakynthos newspaper said, adding that three people had received hospital treatment.

According to Athens National Observatory's Geodynamic Institute, the earthquake struck at 1.54 am and its epicenter was located in the sea, 44 kilometers (27.3 miles) southwest of Zakynthos, also known as Zante, and southwest of Athens.

The United States Geological Survey had reported a 6.8 magnitude earthquake and there were dozens of aftershocks of 5.4 magnitude.

Zakynthos Mayor Pavlos Kolokotsas told the media that the situation was under control and confirmed that no injuries have been reported to him, although landslides triggered by the quake had caused some damage.

He added that schools and day care centers on the island would remain closed on Friday, along with other public services, as a precautionary measure.