Update, 4pm: The search for an abalone fisherman missing off Yanchep has been suspended after rescuers searched for eight hours in stormy conditions.
Up to 17 abalone fishers were rescued today and one man remains unaccounted for off Yanchep Lagoon.
A police spokesman said fatigue and weather conditions were hampering the search.
"You have to understand the conditions are pretty rough... you realistically can only run people for so many hours," he said.
He said the search will continue at first light tomorrow.
Surf Lifesaving crews pulled 12 people from the water at Yanchep between 7.30am and 8am on the opening day of the abalone season.
A further five people are understood to have been rescued from the water at Mullaloo this morning.
A SLSWA spokesman said the missing man was believed to be part of a group of five people who were were abalone fishing at Yanchep Lagoon. It is not yet known how they came to be in the water.
Two helicopters, police Air Wing, water police, two marine rescue groups and police searched for the missing man. Specialist Water Police divers were also heading to the search area.
Surf Lifesaving WA said weather conditions were hampering today's search. However, the search continued until 4pm despite storms.
The Westpac helicopter was been sent to Fremantle to refuel several times during the search.
It is understood the group are overseas visitors. The missing man is believed to be a 20-year-old man from Malaysia.
During the rescues this morning, three people required oxygen and three people were been taken to Joondalup Hospital in a stable condition.
Two of those hospitalised are 29-years-old and one is 24-years-old. A 29-year-old man is expected to be kept in hospital overnight.
There were chaotic scenes at the beaches this morning as people were tossed into the water in rough seas.
There were no flags on the beach at Yanchep this morning. However, volunteer Surf Lifesavers were patrolling the beach.
Locals described the beach as a popular swimming spot. Despite sometimes strong currents, local children have their swimming lessons at the beach.
Yanchep Surflifesaving Club president John Heesters said there is a strong current that many people were unaware of in the lagoon.