"It started to slip over and fell down and crushed the boys and the boat, it all happened in like three seconds from standing upright to snapped in half.
"[The tree] hit the boat and it went under and took the boys down with it.
"We didn't know what to do so I jumped straight in, I thought they were dead.
"It was freezing but adrenaline just took over," Alexander said.
The police spokeswoman said emergency services, including an ambulance, attended but the ambulance was not required.
"Everyone is out of the water now and on Avonside Drive. Everyone is okay," she said.
Last week a woman in Rotorua died after a tree fell onto her vehicle as storms battered the country.