A man is dead and a teenage girl is in Dunedin Hospital in a serious condition after a crash in Riversdale.

Two cars collided at an intersection around 9:30 this morning.

The Otago rescue helicopter was sent to the scene and airlifted the girl and another person with moderate injuries to hospital.

Meanwhile, a 25 year old man died after his car ploughed through a sign in Hamilton around 11:30 last night.

District road policing manager Inspector Freda Grace says the man wasn't wearing his seatbelt and speed is likely to have been a factor.

A person also died in a single car crash in Waiuku in south Auckland earlier this morning.