Surf Life Saving NSW spokesperson Liam Howitt says the organisation is monitoring the situation, but warned beach goers and water users to be mindful of the conditions.

"The swell will slowly build through today (Tuesday, April 17) and by this afternoon will reach between 2.5 and 3 metres," Mr Howitt said.

"These conditions will continue through to Wednesday before slowly easing off around lunchtime.

"This swell also has the potential to build again through Thursday.

"These conditions can be potentially dangerous. 

"We ask that beach goers swim between the flags - there are a number of patrolled beaches along the Mid-North Coast - and our push is certainly for people to swim at a patrolled beach during the week and on weekends."

Mr Howitt said it was critical for holidaymakers and anyone unfamilar with beach conditions to talk with lifeguards and life savers on duty.

He also warned people participating in other coastal activities, including rock fishing, to be cautious when getting on and off rock platforms.

"We encourage the public to be aware of the conditions and if you have any doubts about your ability, talk to the lifeguards and life savers."

Lighthouse Beach is currently the only patrolled beach closed due to the rough conditions.

Meteorologist with weatherzone Craig McIntosh said the dangerous surf warning follows a strong cold front moving through Tasmania on Monday.

"There are south east winds which are pushing gusty coastal winds," he said.

"The maximum temperature for today (Tuesday) would be a 'pretty mild to warm' 25 degrees. That's about one degree above the average for this time of the year.

"Overnight (Monday), the temperature actually dropped to 11.7 degrees at the (Port Macquarie) airport, which is below the 13.9 degree average.

"Winds on Wednesday will shift from the south to the south, south-east and will remain reasonably strong. This will also keep the temperatures in check.

"The minimum tempearture for Wednesday is forecast for the mid-teens but likely to be lower."

Mr McIntosh said the wind direction will change on Thursday - from the north, north-east - which will also see a slight increase in maximum temperatures through to the end of the week.

"Looking further ahead, Friday and through the weekend, is likely to see a potential for a few thunderstorms," he added.