The Bureau of Meteorology has issued severe weather warnings including heavy rainfall, damaging winds, abnormally high tides, and damaging surf for the Sydney Metropolitan area, Illawarra, South Coast and parts of Northern Rivers, Mid North Coast, Hunter, Central Tablelands, Southern Tablelands and Snowy Mountains areas.

There is also potential for periods of torrential rainfall and life-threatening flash-flooding in the Hunter region and Central Coast, Sydney Metropolitan areas, the Illawarra and eastern parts of the Central Tablelands, including the Blue Mountains.

Further, Flood Watch and Flood Warnings have also been issued for Byron Bay, Coffs Harbour, Port Macquarie, Taree, Newcastle, Gosford, Sydney, Katoomba, Lithgow, Wollongong, Nowra, Ulladulla, Eden and Moruya Heads.

Deputy State Emergency Operations Controller, Assistant Commissioner Karen Webb, said emergency services are continuing to assist people impacted by recent and current weather.

"During severe weather events, NSW Police are poised to assist the State Emergency Service, and we are currently working with them to minimise the impact of the storms on the community," Assistant Commissioner Webb said.

"There are currently hundreds of calls for assistance, including trees, boulders or power poles down onto cars and homes, and across roads, as well as power outages and localised flooding impacting various roads and traffic lights."

Assistant Commissioner Webb added that police have also responded to or been made aware of incidents resulting from people taking unnecessary risks or displaying dangerous behaviour.

"I'm disappointed that I need to remind people to act responsibly and not to take risks in these types of conditions, especially when around floodwaters," Assistant Commissioner Webb said.

"We are investigating after a video surfaced online yesterday of a man jet skiing in floodwaters on the Central Coast, which is behaviour so reckless I can barely comprehend it.

"Officers from Brisbane Water Police District and local residents put their lives at risk overnight to rescue five men whose fishing boat capsized as they tried to navigate in the dark to go fishing.

"The water conditions were so dangerous that Marine Area Command were unable to assist, yet none of the men were wearing life jackets, and struggled to swim.

"Thanks to the courage actions of rescuers, the men were safely returned to shore before being treated by NSW Ambulance paramedics for possible hypothermia and cuts and abrasions.

"The SES and Port Stephens-Hunter police have just rescued a 16-year-old boy who was trapped between debris in waist-deep water after falling into the Allynbrook River about 9am.

"The teen was in the water for almost two hours before specialist SES officers were able to free him and safely return him to the riverbank. He's since been taken to hospital with suspected broken ribs.

"Police have also responded to assist dozens of motorists who've become trapped after driving their vehicles into flood waters.

"If you're out and about today, please take extra care and slow down to ensure you arrive at your destination safely," Assistant Commissioner Webb said.

Visit www.livetraffic.com for the latest information on road closures, traffic diversions and potential delays.

NSW SES is also advising they are currently experiencing a high volume of calls for assistance and urge residents to prepare their homes for storm events by:

* Move vehicles under cover or away from trees.

* Secure or put away loose items around your house, yard and balcony.

* Keep at least 8 metres away from fallen power lines or objects that may be energised, such as fences.

* Trees that have been damaged by fire are likely to be more unstable and more likely to fall.

* Report fallen power lines to either Ausgrid (131 388), Endeavour Energy (131 003), Essential Energy (132 080) or Evoenergy (131 093) as shown on your power bill.

* Don't drive, ride or walk through flood water.

* Keep clear of creeks and storm drains.

* If you are trapped by flash flooding, seek refuge in the highest available place.

* Be aware that run-off from rainfall in fire affected areas may behave differently and be more rapid. It may also contain debris such as ash, soil, trees and rocks.

* After bushfires, heavy rain and the loss of foliage can make the ground soft and heavy, leading to a greater chance of landslides.

* Stay vigilant and monitor conditions. Note that the landscape may have changed following bushfires.

For assistance in floods and storms, contact the local SES Unit on 132 500.

In the event of an emergency or a life-threatening incident, always call Triple Zero (000).

More information about staying safe in extreme weather events is available at: https://www.ses.nsw.gov.au.