The death toll from southeast Europe's heatwave has been mounting and up to 500 people were estimated on Tuesday to have died in Hungary the previous week partly due to the heat.

Along Croatia's Adriatic coast, the threat to tourist camps and villages receded as firefighters who have battled blazes for days brought a dozen remaining fires mostly under control.

While temperatures dropped somewhat across the region, strong winds fanned Greece's fires, the deadliest of which spread across the northern coastline of the Peloponnese for a fourth day.

The fire near the coastal towns of Egio and Akrata killed one man late on Wednesday and a woman died early on Thursday after being trapped in her home.

The fire brigade said local residents were searching for another woman, missing since Wednesday, but there were no further details on her condition.

The fire in Greece that started on Monday has ripped through villages torching dozens of houses while more villages are under threat, the fire brigade said, adding several planes and helicopters were battling the blaze.

The area is a popular holiday destination for Greeks, who own holiday homes along the coast.

"This is a fire with a front as long as 30-35 kilometres. It is huge," Egio Deputy Mayor Panagiotis Gousas told reporters. "There are several fire fronts and more houses are in danger."

Regional civil protection chief Yannis Poupis told Greek TV helicopters could not operate over parts of the blaze due to thick black smoke obstructing visibility.

Authorities have closed off the main highway connecting Athens with the port city of Patras on the Peloponnese.

FORESTS RAVAGED

The fire brigade said there were fires all over Greece, from the northern city of Thessaloniki to the southern Peloponnese.

Its resources have been stretched to the limit and army conscripts have been called in to help. One firefighting plane crashed on Monday while battling a blaze, killing its two-member crew, and authorities said it was probably due to fatigue.

Temperatures over 40 degrees baked the country for six consecutive days before Thursday's drop in temperatures to about 38 degrees.

Greece experienced another long heatwave in late June that killed at least 10 people and sent 250 others to hospital with heatstroke.

In Bulgaria, fires have ravaged more than 12,000 hectares (30,000 acres) of forest since last week. Thousands of firefighters and soldiers have been battling blazes that have claimed at least two lives, officials said.

The European Union newcomer has asked its Western allies to send helicopters to help it fight fires in mountains.

"We are calling for help, because the situation is extremely difficult ... and with the wind picking up, it is indeed very serious," disasters ministry spokeswoman Elena Yaneva said.

Sofia also wants to borrow again a Russian water-carrying aircraft which helped put out fires in southern Bulgaria earlier this week, but flew to neighbouring Serbia on Wednesday.

Fires continued to rage in virtually every municipality in the Black Sea country despite a 10 degree drop in temperatures from 40-plus Celsius earlier this week.