Northern Territory Police are searching for a woman who was last seen in the Katherine River.

The 38-year-old female ran into the Katherine River when she sighted police officers after they responded to an incident around 11:00 this morning.

Katherine officers negotiated with the female in an attempt to get her to exit the river however she refused.

The female was sighted travelling downstream before police lost sight of her.

A search and rescue operation is underway.

The matter is being treated as a serious custody incident.

Anyone with information is urged to contact police on 131 444 or Crime Stoppers on 1800 333 000.