Police in Timaru are appealing for sightings of two locals, Nicole Brown, also known as Nicole Smith, and George David Henry Smith.
The police said they were concerned about Ms Brown's safety.
She was last seen near Ayr Street about 5am in her maroon and silver Toyota Hiace van.
Mr Smith, who was 38 years old and very tall, at 2.1m, might be armed, they said.
He had access to a silver Ford Territory, and they were asking anyone who saw him to call 111 immediately.
"As well as hearing from members of the public, we'd also like to hear from Nicole and George," Detective Inspector Darryl Sweeney said.
"We'd welcome any contact from either of them so we know they're OK."