Sydney, December 9 (RHC)-- Fires raging out of control in the Australian state of New South Wales (NSW) have merged into what firefighters dubbed a "mega fire," escalating the destruction of the country's worst fire season on record.

More than 2.1 million hectares (5.1 million acres) have been scorched, 688 homes destroyed, and six people killed since fires erupted across the state in September.  Greg Allan, spokesman for the NSW Rural Fire Service (RSF), said 87 separate fires were burning throughout the state on Sunday.

Cooler weather and more favorable wind conditions have assisted firefighters in containing many of these blazes, but about 50 remain out of control, including the Gospers Mountain "mega fire" near Sydney's northwest outskirts.

"Crews today have worked to slow the spread of fire under the more favourable conditions of easterly winds and undertake back burning where they can ahead of worsening conditions on Tuesday," Allan said.

Temperatures are expected to hit the high 30s to low 40s throughout the state on Tuesday with westerly winds returning, which threatens to place large parts of the state under "severe fire danger."  

The worst of Australia's fire season usually comes in the mid-summer month of January.  "It was a very fast, very early, very destructive season," Allan told Al Jazeera. "In fact, the amount of hectares already burned is more than the previous three seasons combined, and the season is not over yet."