Emergency services are at Haumoana Beach where a woman is suspected to have drowned, and two children were taken to hospital.
The co-ordinated effort were searching between 200 and 500m from the shoreline. Search efforts would continue until it was dark.
A police spokeswoman said they were notified around 4:50pm of three people that were in trouble in the water at Haumoana.
Two children made it back on shore and were taken to hospital, however a woman remains outstanding and a search is underway to locate her.
Hastings resident George Araia was one of the last to see the missing woman.
He had been fishing with a friend at the confluence of the river and beach all day.
From his spot he had seen the two children playing. He believed the missing woman had walked across the beach past him and his fishing companion.
"We saw her walking toward her grandchildren. Nothing seemed strange."