The worsening smoke haze from the NSW bushfires has forced officials to call off barrier trials at Gosford and Randwick.

Tuesday's Randwick trials have been rescheduled to Friday in the hope Sydney's air quality improves but the heats at Gosford have been abandoned with no suitable replacement date available.

The air quality in Sydney on Tuesday has been described as hazardous.

Temperatures are predicted to reach 40 degrees in parts of NSW and western Sydney before a cool change arrives.

But the southerly is not expected to make any improvement to the air quality.

Several race meetings and sets of trials have been lost over the past few weeks particularly in the Mid-North coast region.

Fires continue to burn on the east coast of the state and the Blue Mountains close to Sydney.