Sydney has been blanketed by fog on Monday morning, with drivers warned about poor visibility and ferry services cancelled.

The Bureau of Meteorology warned that road conditions would be dangerous and motorists were advised to take extreme care.

“Fog developed in the western suburbs, and it’s currently making its way eastward and moving over eastern suburbs, so expecting driving conditions to be a little bit hazardous,” meteorologist James Taylor said.

“When we get cool air and clear sky it’s good for trapping smoke down close to the surface, it’s also very good conditions for fog formation.”

F3 Parramatta River, F4 Pyrmont Bay and F8 Cockatoo Island ferries were not running due to heavy fog.

There was no forecast for when ferry services would resume.

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The Electrical Trades Union advised members to down tools on Monday if they were affected by smoke.

The fog had started to clear by 9am but was being replaced with smoke from hazard reduction burns.

A poor air quality alert was issued for Sydney’s east and south-west, with ‘poor’ or ‘very poor’ conditions at Chullora, Randwick, Earlwood and Lidcombe.

People in those areas were advised to avoid outdoor exercise, while those who are sensitive to smoke were told to stay indoors as much as possible, with windows and doors closed.

The Rural Fire Service is carrying out hazard burns in areas including Sutherland, Campbelltown, the northern beaches and the Blue Mountains.

A spokesperson for the RFS said it was “conscious of smoke impact” but that it was important to conduct these hazard reduction burns to areas not affected by the 2019-2020 bushfire season.

“We’ve worked closely with NSW Health to try to reduce the impact of smoke across, in particular the Sydney basin, but also surrounding areas,” Angela Burford said.

Larger planned burns have been broken up and carried out across several days in an effort to reduce the smoke impact.

Smoke is likely to linger for most of this week, depending on the rain forecast for mid-week, which will affect the RFS’ hazard reduction efforts.

-ABC