Greek Prime Minister Alexis Tsipras on Monday paid his first visit to the area ravaged by the country's worst ever wildfires, as anger mounts over his government's response to the disaster which has claimed scores of lives.

His trip, a week after the fires broke out, was not announced beforehand in what local media said was a bid to avoid protests by residents of the hard-hit seaside communities east of Athens -- Mati and Rafina.

Tsipras visited the area for an hour, his office said, meeting with local authorities, fire brigade and army officials, and volunteers amid fears the death toll could exceed 100.

"We thank you for all you are doing," the PM told rescuers, some of whom have been mobilised for three straight days, recovering charred bodies, maintaining security and working -- amid dwindling hope -- to locate survivors.

"Keep morale high," he told a firefighting officer in footage exclusively aired by state broadcaster ERT. "Let the barbs fall on us, not you."

On his Twitter account, Tsipras said he had "boundless respect" for those who fought "against the odds" in the flames.

But his government has faced mounting criticism as residents battle to resume their lives with the help of the authorities and volunteers.

The death toll rose to 91 on Sunday and another 25 people remain missing, but many may be among 28 victims whose bodies are being examined by forensic pathologists and have not been identified, local authorities said.