The Bureau of Meteorology says residents in the New South Wales Hunter region should avoid swimming at local beaches today with an east coast low resulting in huge seas along the east coast.
Heavy rain and gale force winds are also expected along the coast today, with conditions expected to ease tonight.
Newcastle Council has issued a warning to beachgoers to only swim in patrolled areas and to speak with lifeguards before heading into the water.
Meteorologist Grant Conway says tomorrow is looking much better.
"It will generate quite high seas and that will affect the coastal regions," he said.
"Also, we have a gale wind warning for the Hunter's coastal waters.
"Dangerous surf conditions are persisting and that makes it hazardous for swimming, surfing and rock fishing and that's associated with this low pressure system off the coast.
"There is a possibility of some quite heavy falls around the coastal fringe."
A charity water ski event from Sydney to Newcastle has been postponed due to the weather conditions.
© ABC 2013
16:38 EST Organisers of the Mulga Bill Quick Shear at Yeoval, in Central West New South Wales on the weekend, were a bit nervous about the weather on Saturday morning; there'd been good rain on Friday night and they didn't have a 'Plan B' if things didn't clear up.