Christmas unfolded with a massive swell for big-wave surfers in what is becoming a memorable winter for large surf.

Waves with face heights of 30 feet or more pounded O'ahu's North Shore, forcing lifeguards to rope off beaches with tape carrying a warning for people not to enter. Waves sent sand and water over Kamehameha Highway at Laniäkea, Chun's Reef and Rockville .

"That's big. That's really big," said bodyboarder Surl Gunderson, as he stood behind cautionary yellow plastic tape preventing access to the water at 'Ehukai Beach Park.

Gunderson, 20, was among the 75 or so people who watched silently as giant waves unfolded far offshore, breaking in places rarely seen. Pipeline was unrecognizable as waves washed over its reef. Gunderson said he probably would look on the leeward side for smaller surf.

The unusually large swell was caused by hurricane-force winds northwest of Hawai'i earlier this week. The National Weather Service is projecting the waves will decline today to 15 to 25 feet on the North Shore.

The weather service forecasts the swell will continue diminishing through tomorrow with a new northwest swell arriving at the start of the work week.

But yesterday, thousands of people took time off from holiday celebrations to view the swell. Crowds gathered at various beaches, mesmerized by a cauldron of waves and white water that seemingly stretched to the horizon.

Stop-and-go traffic heading to Waimea Bay from Hale'iwa stretched past Laniäkea. A light haze from the spindrift off the tops of waves hung over the coast.

The city's Ocean Safety and Lifeguard Services Division also encouraged people to stay out of the water on the leeward side of O'ahu. On Maui, Ho'okipa Beach Park was closed when water from waves estimated at 20 to 25 feet reached the pavilion area.

Honolulu Emergency Services Department spokes-man Brian Cheplic said ocean safety officers were busy during the day, undertaking 2,400 warnings, 25 rescues and 20 assists on the north and west shores.

Some observers said yesterday's swell was reminiscent of one Dec. 8, when the Quiksilver in Memory of Eddie Aikau was run. That contest was run in wave-face heights of 35 to 50 feet.

North Shore surf photographer Vince Cavataio said yesterday's swell was a tad smaller, though some sets approached the size of the waves during the contest.

One set came through in the early afternoon that had waves that unfolded across the bay, catching most surfers inside of the closeout. That didn't happen during the Eddie, Cavataio said.

"I was just in survival mode right then," said Christian Jensen, a 33-year-old Sunset Beach resident who was out at the time and dove off his board, only to surface and find it in two pieces.

The 10-foot Eric Arakawa big-wave "gun" was snapped pretty cleanly in two, aside from all the fiberglass on the bottom of the board being stripped away.

Bill Whalley, 29, was among hundreds of people who gathered around the arena-like bay who saw the closeout set. He said five boards washed up on the beach after the waves and that more than half of the 20 or so surfers who had braved the monstrous waves came in afterward.

"There was nothing like that during the Eddie," said Ron Fumar, a 27-year-old Hale'iwa resident, who estimated the closeout waves' height at 30 feet.

That didn't stop others from paddling out, including 24-year-old Thomas Portet, who borrowed a 9.5-foot pintail gun for his first surf session at Waimea. Most people elected to stay on the beach, saying this winter surf season has been a notable one for giant surf.

Fumar said there already had been at least two days of exceptionally large swells since the official start of winter on Dec. 21.

Whalley also agreed the North Shore season has been a good one for big surf.

"It seems pretty good compared to a couple of winters ago," he said.

Jensen said there had been four days of big waves so far this season at Waimea, compared with last year when he said the bay never got more than 18 feet. "It's been a good winter so far."