Updated 9.40pm

Around a dozen homes burned and five people were hospitalised with breathing problems on Saturday as firefighters fought a forest fire near Patras, Greece's third-largest city, authorities said.

Some 145 firefighters, 50 trucks, eight firefighting planes and helicopters have been mobilised to extinguish the fire in the Zeria region in the Peloponnese, about 210 kilometres west of Athens, the firefighting service said. 

The authorities evacuated people from four villages in the region as well as from the tourist resort of Loggos on the coast.

Around a dozen homes burned and five people experiencing breathing problems were transported to hospitals in the region, the civil protection authority said.

Hospitals in Patras and the neighbouring city of Aigio had been put on notice to admit any injured people, while the coastguard has been on standby to rescue any swimmers overcome by smoke.

The Greek press agency ANA said the highway between the Peloponnese and continental Greece had been closed.

Greece is hit by forest fires every summer, but experts have warned that global warming increases both their frequency and intensity.

Greece has been in the grip of another heatwave since Friday, with temperatures hovering between 42 and 44 degrees Celsius, weather forecasters say.

Several days ago, a fire ravaged Mount Penteli, close to the capital Athens, but caused no casualties.

It was the same area where a fire in July 2018 went on to claim 102 lives in Greece's worst-ever toll from a forest inferno.