Fast-moving wildfires have swept across hills in the searing heat outside the Greek capital Athens, forcing authorities to close motorways to help protect an oil refinery.

Water-dropping planes and helicopters flew low through a blanket of smoke tinted orange by the sunset to try to contain two wildfires to the west of Athens before nightfall.

The European Union pledged additional assistance, while forecasts indicated more extreme heat was on the way.

A firefighting helicopter flies through smoke as people look on in Mandra west of Athens
A firefighting helicopter flies through smoke as people look on in Mandra, west of Athens (Petros Giannakouris/AP)

Italy and France were each sending two firefighting planes to help Greece cope.

The planes and their teams are part of an EU civil protection mechanism, and they will join some 30 Romanian firefighters already stationed in Greece as part of a seasonal EU fire programme, European officials said.

Fire Service spokesman Vassilis Varthakoyiannis said the main fire near Athens rapidly became a major crisis.

“The Fire Service had to intervene in many instances to get people out of their homes,” the spokesman said.

Officials cancelled holidays and leave for firefighters, while Greek prime minister Kyriakos Mitsotakis cut short a visit to Brussels and returned to Athens to meet with the heads of the Fire Service and Civil Protection Agency.

Wildfires continued to burn out of control on Tuesday to the north and west of Athens, including a blaze near the resort town of Loutraki, where more homes were damaged and evacuations were expanded.

A police car blocks a road as the smoke from the wildfire engulfs the village of Agia Sotira, near Athens
A police car blocks a road as the smoke from the wildfire engulfs the village of Agia Sotira, near Athens (Thanassis Stavrakis/AP)

In the fire-threatened town of Mandra, west of Athens, police ran through narrow streets to help residents into cars as the flames approached.

Earlier, police helped nuns leave a hilltop Orthodox Christian monastery that was also under threat.

Several smaller fires also broke out closer to the capital, where winds remained moderate but where scrub and forest land were dried out by extreme temperatures last week.

Authorities said sections of two motorways linking Athens to the western city of Corinth were closed to give firefighters better access to the fires and to stop the flames from approaching a major oil refinery.

Greece also activated a rapid mapping evaluation system, which uses EU satellite data to assess fire damage.

A second heatwave is expected on Thursday, with temperatures as high as 44C expected in central and southern parts of the country by the end of the week.