Warragamba Dam nearing capacity as heavy rain and wild winds lash NSW

Heavy rain and strong winds are battering much of the New South Wales coast causing flash flooding and landslips.

Strong ocean swells have rocked the Manly Ferry travelling across Sydney Harbour, and hundreds of SES workers are responding to calls across the state.

The Warragamba Dam on the outskirts of Sydney's south-western suburbs is almost full. This time last year it was at 48 per cent.

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"It is at near capacity and we will be making sure what ever plans for flood response as ready to go,' NSW Police and Emergency Services Minister David Elliott said today.

"It's only recently the dam has gone back up to 96 per cent capacity and that's the reason why we have these response plans."

There is a severe weather warning for heavy rain and damaging winds for the Central Coast, Mid-North Coast and Hunter regions.

A warning for damaging winds is in place for Southern Tablelands, South West Slopes, Snowy Mountains and ACT.

Mount Elliott on the Central Coast has recorded 192mm of rain in the past 24 hours, while Williamtown has recorded 129mm, and there has been 128mm at Gosford.

At Narara, also on the Central Coast, a taxi driver was filmed driving through floodwaters, while at Holgate the driver of a BMW had to be rescued after their car was stuck in deep water.

Across the state more than 200 SES volunteers are responding to calls, most of which relate to leaking roofs and other small jobs.

In the past 24 hours there have been between 120 and 150 requests for assistance, Mr Elliott said, and at least one flood rescue.

At Great Mackerel Beach on Sydney's Northern Beaches, at least one home has been badly damaged, and others are at risk.

NSW Police and the SES have evacuated the residents of 15 homes. The damage in the area is being assessed by Northern Beaches Council officials.