Police are looking for a dangerous Nelson prisoner who's on the run for a second time, after escaping police custody.

Ihaka Kawana escaped this morning.

He's described as Maori, 176-centimetres tall, and wearing a brown T-shirt and black jeans.

He previously slipped away from the District Court in October last year, leading to a large search.

The 22-year-old has a lengthy criminal history, in 2011 he was sentenced to 60 hours community service for wielding a pair of vice grips in a street fight.

Four years later he was convicted over two aggravated robberies on a Nelson dairy, where the shopkeeper told the court he thought he was going to die.

Police said he should be considered dangerous and shouldn't be approached.