Five people are reported to have died after a boat in New Zealand capsized, reportedly after a collision with a whale, local media reported.

New Zealand’s public broadcaster RNZ (Radio New Zealand) reported on Saturday that the boat capsized off Goose Bay near the South Island town of Kaikoura.

Eleven people were on board the vessel when it overturned and five bodies were later recovered by emergency services workers, RNZ reported, citing local police. Six people were rescued.

“Police said the boat overturned after a ‘collision’, but could not confirm what it collided with,” the broadcaster reported.

Kaikoura’s Mayor Craig Mackle told The Associated Press news agency that the sea was calm at the time of the accident and the assumption was that a whale had surfaced from beneath the boat and flipped it.

Mackle said there were sperm whales in the area and also some humpback whales travelling through at the time.

The boat that capsized had been chartered by a group of women.