A Hato Hone St John spokesperson said one person in a serious condition was being taken to Rotorua Hospital.
Two ambulances, one operations manager, and one rapid response unit went to the crash, the spokesperson said.
A Fire and Emergency NZ spokeswoman said three fire trucks, a support vehicle and a boat also went to the scene.
A person who answered the phone at the Emery Store told the Rotorua Daily Post a vehicle went into the lake on the sharp bend near the store.
“We heard a big noise, me and my husband said ... what happened?
“We ran quick outside the shop. Oh god, it’s crazy.”
She said there were people in the vehicle but didn’t know how many.