A state of emergency has been declared in New South Wales as bushfires burning west of Sydney threaten to worsen over the coming days.

Around 60 fires are burning across the state but, according to the Rural Fire Service several in the Blue Mountains may join up to become a single, bigger fire that could then threaten a number of communities.

The NSW State Premier, Barry O'Farrell, said his declaration followed a weather forecast for the coming days worse than expected.

It has given the emergency services the powers to deal with situations as they arose.

RFS Commissioner Shane Fitzsimmons said the fire near Lithgow, west of the Blue Mountains, will continue to burn for several days and that a number of communities in its path may be told to evacuate.

One man has died and hundreds of homes have been destroyed since the fires took hold last Thursday, according to the RFS.

The last time a state of emergency was declared in Australia's most populous state was during flooding in March 2012.