In Hawaii, a couple walks along the beach as giant waves break along the Waimea Bay on the north shore of the Oahu. Surfers have flocked to the area amid reports that waves of up to 50 feet are expected until Wednesday. (REUTERS)

HONOLULU (AP) – Thousands of spectators and surfers are flocking to Hawaii's beaches to see the biggest waves in years crash ashore.

Heavy traffic backed up for several kilometers Monday along roads leading to Oahu's North Shore. Some of the world's most daring surfers took on the powerful and dangerous waves, which forecasters say could reach heights of 50 feet (15 meters).

The surf grew so large that a few beaches on Oahu and Maui were closed because lifeguards feared inexperienced sightseers could drown, according to state officials.

“After the water comes in, it can drag you back out with it,” said Eric Basta, a manager at Surf N Sea in Haleiwa. “Be mindful of how powerful the surf really is.”

As violent as the waves were, they may grow in strength by Tuesday, according to the National Weather Service.

The high waves are expected to continue through Wednesday.

A legendary big wave surfing contest, the Quicksilver in Memory of Eddie Aikau, may be held Tuesday for the first time since 2004 if waves reach a minimum of 40 feet (12 meters), organizers said. The event is only held in perfect conditions, and the waves weren't quite big or smooth enough yet Monday.

“The swell energy is continuing to grow, and the waves may get larger,'”said Robert Ballard, a forecaster for the National Weather Service. “A large storm over the North Pacific has sent a wave train at us.”

Hawaii hasn't seen such large waves since 2004 or 1998, he said.

Teams of tow-in surfers – who use jet watercraft to race into waves too big to paddle – are flying to Maui from Brazil, South Africa and Australia, The Honolulu Advertiser reported.