The centre of a New Zealand town has been evacuated after boxes of unstable dynamite were dumped on the steps of the local police station.

Police said about 100 sticks of dynamite were found in wooden boxes at the Balclutha police station on the South Island early this morning.

"The dynamite was sweaty, wet and thought to be unsafe," police said in a statement.

"The Balclutha police station and surrounding area has been evacuated and cordoned off until army explosive experts travel to Balclutha and dispose of the dynamite."

Radio New Zealand reported that police believed the dynamite was left by a farmer unsure of how to dispose of the explosives, rather than someone intending to blow up the police station.

- AFP