A person has been winched out of a South Island national park by helicopter after being hit by a falling tree branch.

Ambulance teams were alerted to the incident along the Kepler Track in Fiordland National Park, near Manapouri, earlier this morning and called in a rescue helicopter.

The chopper was able to winch the person out at about 12.15pm, a police spokeswoman said.

St John said the person was in a serious condition and being flown to Dunedin Hospital.