A search is underway for a brother and sister, aged 10 and four, who went missing after their mother left them unattended for 15 minutes in a park in NSW’s Northern Rivers region.

Police say William and Savannah Bradbury were at Colley Park in Casino about 3pm on Thursday when their mother left them to visit a nearby home, finding them gone when she returned.

Police conducted extensive patrols but were unable to find the children who may have been seen by a witness leaving the park on their own.

Police and State Emergency Service personnel have conducted door knocks in the area and anyone who sights the children is asked to contact police immediately.

More to come