At least 400 French firefighters were battling a wildfire of "exceptional scale and virulence" in forest outside Paris for the second day straight amid a "red" heatwave alert in the Ile-de-France region, 40 miles southeast of the capital. Photo by Frank Desprez/Seine-et-Marne Fire and Rescue Service/EPA

July 13 (UPI) -- At least 400 French firefighters were battling a wildfire of "exceptional scale" in a forest south of Paris for the second day straight, authorities said Monday as the region sweltered under a severe "red" heat wave alert.

The blaze 40 miles southeast of Paris has already burned 800 hectares of the Forest of Fontainebleau, forced the evacuation of 900 homes, partially shut the country's main north-south autoroute and disrupted rail travel, with the interior minister warning that it may have been set deliberately.

"The fire began at several points at the end of yesterday afternoon -- around 10 points, which would suggest it could have been voluntary in origin. I won't say more because an investigation is ongoing," said Laurent Nunez.

No one has been hurt and no properties destroyed so far.