Port Otago is launching its own investigation into a serious incident which left a young worker in hospital.

A male employee was rushed to Dunedin Hospital in a serious condition after the straddle carrier he was driving toppled over.

WorkSafe New Zealand is also investigating.

The incident has prompted calls from the Maritime Union for a health and safety inquiry of the whole industry.

Police and St John staff attended, but they're not releasing much detail as the matter's under investigation.

It's understood the male worker's a 26 year old local who's been at the port for years.