"I've been here 34 years and never seen anything like it," senior Newcastle beach inspector Warren Smith said.

"It bodysurfed a wave to the shore, made its way up through the flags and plonked itself up on one of the rocks."

Hundreds of onlookers marvelled at the unexpected visitor, who has been spotted by lifeguards at Nobbys Beach several times during the past month.

It is believed the water temperature of 17 degrees, two degrees higher than this time last year, has drawn a good supply of fish to the area and lured the seal to Newcastle's shore.

The warm winter water has also attracted some of the biggest winter crowds recorded at Newcastle beaches this season.

More than 8500 people packed Nobby's Beach as part of World Youth Day celebrations last weekend, the largest crowd since the Pasha Bulker grounded itself there in June last year.

"It was phenomenal," Mr Smith said.

The past three weekends have had an average of 1500 beachgoers hit the sand at Nobbys Beach, and another 1500 at Bar Beach.

"On a weekend we can have 3000 people on the Nobbys promenade, 1500 on the beach and up to 400 in the water," Mr Smith said.

He said fine weather combined with warmer water was behind the large turnouts, and quite often it was warmer in the water than out.

"We normally don't see water temperatures like this until early September," Mr Smith said.

Big crowds are expected to hit the coast again at the weekend with the temperature tipped to reach 23 degrees on Sunday.