The premier of Australia's New South Wales has declared a state of emergency for the next 30 days to give emergency services the authority to force evacuations in areas hit by the worst bushfires in several decades.

Premier Barry O'Farrell told local media that the measure would be implemented across the state on Sunday, as hotter and drier than expected weather conditions fanned huge fires in the Blue Mountains west of Sydney.

Australian fire crews stepped up containment efforts around several major bushfires with the weather forecast to deteriorate and officials warning of "unparallelled" danger from the worst conditions in 40 years.

More than 200 homes have already been destroyed and another 120 damaged by the fires which broke out across New South Wales state earlier this week, fanned by extremely high winds.

The worst of the fires, in the Blue Mountains, plunged Sydney into an eerie midday darkness as plumes of smoke and ash filled the sky.

One man has died so far trying to protect his property.

Firefighters had a reprieve on Friday and Saturday with an easing in the weather, but containment and property protection efforts were ramped up on Sunday ahead of a forecast deterioration in conditions set to include warmer temperatures and 100kph winds.

'Unprecedented conditions'

NSW Rural Fire Service Commissioner Shane Fitzsimmons said there would be several extremely difficult days ahead for fire crews, with conditions unprecedented in their danger to property and life.

"We've got what would be unparallelled in terms of risk and exposure for the Blue Mountains and Hawkesbury communities throughout this week," Fitzsimmons told reporters.

"If you are to draw a parallel, and it's always dangerous to draw a parallel, at best you'd be going back to time periods in the late 60s."

"The reality is, however, these conditions that we're looking at are a whole new ball-game and in a league of their own.

An emergency warning was issued for the Blue Mountains village of Bell on Sunday morning, with residents urged to evacuate if they were able or "take shelter in a solid structure when the fire front arrives".

A total fire ban was in place in the Greater Sydney and three other regions across the state until further notice.

Assistant police commissioner Alan Clarke said mandatory evacuation orders would be enforced in some areas, describing the risk as "far more extreme" than in past fires.

"At the end of the day we hope we have buildings standing, but if we don't have buildings standing we don't want bodies in them."

"It's important to understand that the single tragedy that we've had in these fires so far has been the tragic circumstances where an individual chose to remain and fight a fire. It is extremely dangerous circumstances."

Bushfires are common in Australia's summer months, which run from December-February, but an unusually dry and warm winter and record spring temperatures has seen the fire season start early.

Source: Agencies