A woman, believed to be from a Sydney surf club, and a child are missing after the boat they were on capsized on a river in NSW's west.

Emergency services are continuing to search the Gwydir River, near Bingara, for the child, aged 5, and the woman, 55.

The pair were among seven people on board the boat when it tipped over this morning.

Police said five people made it to shore, but the two remained unaccounted for.

Initially it was thought the incident happened on Copeton Dam but a State Water spokesman told Fairfax Media the incident occurred about 35 kilometres downstream of the dam on the Gwydir River, accessible only by a four-wheel-drive access road.

He said staff were contacted by police at 11.30am and asked to stop releasing water from Copeton Dam and their instructions were acted on immediately.

The spokesman said about 1600 megalitres a day was being released from the dam, but all releases had been stopped until further notice.

It is believed the child was wearing a life jacket but not the woman.

The pair are believed to be from a Sydney surf club, which had a large group of people camping at the area.

A spokesman from Surf Life Saving NSW said they had been in touch with police and would be releasing a statement shortly.

A combined land, air and water search was under way, including police divers sent from Sydney.

Officers from the outlying New England police command were called to help their Barwon colleagues.

SES North West regional controller Phil Lalor confirmed SES volunteers were assisting with the search.

Eight volunteers, two SES vehicles and a boat were at the scene.

Adverse conditions have prevented searches on part of the river.

Northern Daily Leader and AAP