A woman is dead after an Anzac Day double shooting in Invercargill.

A second victim wounded by gunfire last night is in hospital with serious injuries.

Police said a person was now in custody and helping with the investigation. They were not looking for anyone else.

The fatal shooting happened just after 8pm on Otepuni Ave in the suburb of Newfield.

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A witness described seeing a man pull up on a bike, put on a balaclava and pull something out from his jacket shortly before the shooting.

He said "there were cops everywhere".

"There were cop cars at each end of the cordon, a couple of ambos and a fire engine turned up at one point."

The man said police with torches could be seen searching an area outside the commercial building.

Local Terry Brown said he saw a "chap" bike past, and had an inkling something was off. "It didn't look right. It looked a bit suspicious," he said.

His interest was piqued when the man took off the top he was wearing and put on another, darker piece of clothing before cycling down Otepuni Ave.

Within half an hour the cyclist rode back past his house, still wearing the dark clothing.

This morning the street remained closed.

A police spokesman said they would be making more inquiries today.