UPDATE: The 11-year-old girl missing in Gisborne has been found alive and well.
The girl reportedly went to swim with friends and didn't know people were looking for her.
She was reunited with her family when she walked along the beach to her mother, who says she thought it was an apparition.
Waikanae surf lifesaver Gary Stevens said he arrived at the beach about 5.30pm to see up to 30 people searching the water for the girl.
He understood the girl was last seen in waist-deep water, near the mouth of Turanganui River.
"No one seems to know what happened," he said.
"About 100 people, including surf lifesavers, coastguard, police, St John and members of the public, have been looking for her.
"There's only about half an hour or an hour of daylight left so the search will probably have to stop soon."
He understood the girl's parents had alerted emergency services after about 20 minutes of her not returning home.
It was a beautiful day and several people had been at the beach, he said.
Police said earlier the national dive squad was on standby and the search would continue until dark.
Eastland Port and the Gisborne District Council began a safety review of Butlers Wall after a 19-year-old hit his head on a rock during a wall jump and suffered a serious spinal injury.
Port general manager Andrew Gaddum said new signage would be put up to deter people jumping off the wall.