Greek firefighters are struggling to contain scores of wildfires stretching nationwide, as the week's death toll from the raging blazes rose to 21.

The Greek fire brigade on Friday said they had found the body of a man in the same area in Evros, northern Greece, where the first victim of the week's fires had been found on Monday.

The bodies of another 19 people believed to be migrants, two of them children, were found in the area earlier this week.

The Evros region is a regular entry point for migrants and local border guards had warned that more asylum-seekers could have been trapped by the fires.

An elderly shepherd died in another fire in Boeotia, north of Athens on Monday.

"Greece is experiencing the most difficult year in terms of climate conditions since the start of the collection of meteorological data," government spokesman Pavlos Marinakis said during a regular briefing.

He added that over the last week the fire brigade had to deal with 516 new outbreaks.

The Evros front, burning since Saturday, remained the most difficult challenge for firefighters on Friday.

Suspicion of arson

"Unfortunately Evros is the most active part of all the fronts we are facing at the moment, and perhaps the most difficult section that we will face today," fire department spokesman Yiannis Artopios told state television ERT.

Authorities blamed arsonists for the multiple fronts that have emerged simultaneously in the country during the past few days.

Artopios said investigations into the arsons now involve the national intelligence service. A 45-year-old man was arrested on suspicion of arson on Thursday.

This year's burned land area is three times larger than the annual average since 2006, according to the European Observatory of Forest Fires.