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."
The first moment they realised something was wrong was when they heard emergency sirens, and heard about the children being in trouble.
Mr Araia spent the afternoon helping in the search for the missing woman. He said the two children had been found about half an hour apart.
The search is being co-ordinated by police, and involves other emergency services, Coastguard, surf lifesaving, and a helicopter.
A Haumoana resident, who saw the family just before the incident, said they appeared to be playing, and nothing seemed to be wrong.
He said in the space of ten minutes between him leaving to speak with some friends and returning, the two children had gotten into trouble. He did not see the woman.
He watched emergency services bring two children to shore, who he thought were around the ages of 7 and 12.
Police waders are scouring the river mouth of the Tukituki River, which lets out near the beach.
A St John Ambulance spokeswoman said they were called just before 5pm to a water incident on Domain Road, Haumoana.
"We sent one ambulance and transported two patients with moderate injuries to Hawke's Bay Hospital."
They could not provide the patients' names or genders.
More to come.