Porto Germeno, Greece - Two fire helicopters collided in Greece on Sunday as forces battled multiple wildfires that have devastated swathes of land, with Prime Minister Kyriakos Mitsotakis warning of "extremely difficult" days ahead.

The hired Bell helicopters collided while battling a wildfire in the Psatha area west of Athens, the fire service said on Sunday.

"Search and rescue teams were immediately mobilized to locate and assist the crews," it said.

State broadcaster ERT reported that one crewmember had been found safe, while rescuers were searching for the second.

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TV footage showed one of the helicopters explode and plunge to the ground in flames after an apparent rotor collision.

Mitsotakis earlier said Greece was experiencing "extreme weather conditions" with winds that had reached 100 kilometers (60 miles) an hour.

"When the winds blow with such force, even the dozens of aircraft we have at our disposal cannot operate safely," he wrote on Facebook.

Nearly 500 firefighters were battling blazes around the popular coastal village of Porto Germeno, 70 kilometres northwest of Athens, the fire department said.

They were attempting to keep the fire from approaching the western outskirts of Athens after it scaled a mountain overnight.

Some 100 firefighters were fighting another blaze in Aigialia in the northern Peloponnese.

A new fire broke out late Saturday on the Ionian Sea island of Cephalonia, Greece's popular holiday destination.

A 44-year-old man was arrested Sunday in Cephalonia on suspicion of deliberately starting the fire, according to the Greek news agency ANA.

The National Observatory's climate tracker meteo.gr said early estimates indicated that over 6,500 hectares (16,000 acres) had been burned in separate fires on the Gulf of Corinth, which also swept Porto Germeno.

It added that meteorological conditions remained adverse "mainly due to strong northerly winds, which, however, have partially weakened compared to previous days."