A total of 171 firefighters were to arrive on the French overseas territory in the southwestern Indian Ocean, local prefect Michel Lalande said, bringing to 400 the number of French reinforcements sent to help battle the blaze.
The fire erupted on October 11th in La Reunion National Park and according to local officials has already affected more than 2,600 hectares (6,400 acres) of land.
The park, which covers more than 100,000 hectares or 40 percent of Reunion, was last year granted World Heritage Site status by UN cultural agency UNESCO, which praised its "variety of rugged terrain and impressive escarpments, forested gorges and basins creating a visually striking landscape".
UNESCO raised concerns about the fire in a statement last week, saying it was "the worst the area has seen in 20 years."
"Key areas of endemic plants seem to be seriously affected as well as other key micro-habitats for biodiversity. Among wildlife, several rare species are under threat," UNESCO said.
French environmentalists have accused authorities of reacting too slowly to the fires.
The French Green Party on Sunday denounced "the drastically inadequate response" by state and local authorities to the fire, which it called "a true national catastrophe".