Wildfires intensified across southern Europe on Wednesday, with a round-the-clock battle to protect the perimeter of Greece's third-largest city and at least three deaths reported in Spain, Turkey and Albania.

Outside the Greek port city of Patras, firefighters struggled to protect homes and agricultural facilities as flames tore through pine forests and olive groves. Tall columns of flames rose behind apartment blocks on the outskirts of the city, while dozens of vehicles were torched as fire swept through a nearby impound lot.

"Today is another very difficult day with the level of fire risk remaining very high across many parts of the country," Fire Service spokesperson Vassilis Vathrakoyiannis said. At least 15 firefighters were hospitalized or received medical attention for burns, smoke inhalation or exhaustion, he said.

As water-dropping planes and helicopters swooped overhead, residents joined the effort, beating back flames with cut branches or dousing them with buckets of water.

Resources stretched thin

Firefighting resources were stretched thin in many affected countries as they battled multiple outbreaks following weeks of heat waves and temperature spikes across the Mediterranean region. On the Greek island of Chios, exhausted firefighters slept on the roadside following an overnight shift.

Aircraft rotated between blazes on the western Greek mainland, the Patras area and the island of Zakynthos. Athens also sent assistance to neighbouring Albania, joining an international effort to combat dozens of wildfires. An 80-year-old man died in one blaze south of the capital, Tirana, officials said Wednesday.

Residents of four villages were evacuated in central Albania near a former army ammunition depot. In the southern Korca district, near the Greek border, explosions were reported from buried Second World War-era artillery shells. Authorities said dozens of homes were gutted in a central region of the country.

Spanish Prime Minister Pedro Sánchez expressed condolences after the death of a firefighting volunteer in the hard-hit Castile and León region north of the capital, Madrid, where thousands have been displaced by evacuations.

Evacuation centres were filled to capacity in parts of central Spain, with some spending the night outdoors on folding beds. The most severe fires pushed northward into more rural areas, where some residents hosed the walls of their homes to protect them from fire.

Services along a high-speed rail link between Madrid and the northwestern Galicia region were suspended after fires got close to some sections of the tracks, state rail company Renfe said.

In Turkey, a forestry worker was killed Wednesday while responding to a wildfire in a southern region, officials said. The Forestry Ministry said the worker died in an accident involving a fire truck that left four others injured.

WATCH | Fires and historic heat: 

Historic heat fuels fires across Europe

Record-high temperatures across Europe are fanning wildfires across the continent. Experts say a warming climate and an increase in flammable vegetation from rural depopulation are major factors.

Turkey has been battling severe wildfires since late June. A total of 18 people have been killed, including 10 rescue volunteers and forestry workers who died in July.

In France, which is recovering from recent massive fires in the southern regions, temperatures of up to 42 C were expected for the third consecutive day. Officials issued weather alerts giving local authorities discretion to cancel public events and cordon off areas with high fire risks.

To the southwest of France, a blaze in Trancoso, Portugal, which has been burning since Saturday, got worse overnight after lightning reignited an area that was thought safe, the civil protection service said.

Authorities across European countries have cited multiple causes for the fires, including careless farming practices, improperly maintained power cables and summer lightning storms.

Law enforcement officials in North Macedonia also cited indications of arson, motivated by rogue developers. Firefighters struggled to contain a blaze at a nature reserve outside the capital, Skopje, on Wednesday.

The European Union has rushed aid to fire-hit countries, including non-member states, with ground crews and water-dropping aircraft. Much of the recent effort was concentrated on Montenegro, where major wildfires continued to burn in rugged areas near the capital, Podgorica.

"Natural disasters know no borders," Ljuban Tmusic, head of Montenegro's civil protection agency said. "In Montenegro, the resources we have ... are clearly not enough."