Emergency services responded to a family harm incident on Henderson Ave, Flaxmere at 11.10pm on Saturday.
A police spokeswoman said one person had been arrested and was in custody after one person suffered serious injuries.
A Hawke's Bay District Health Board spokeswoman confirmed a female in her late 40s was in a critical condition, last night in intensive care at the Hawke's Bay Hospital.
Meanwhile, emergency services were called to a "well-involved" fire on Ramsey Cres, Flaxmere at 4.55am today.
Fire communications shift manager David Meikle said four appliances; two from Hastings and two from Napier attended the blaze.
One person was treated for smoke inhalation by St John's Ambulance, but did not need to go to hospital.
Hastings Fire Service senior station officer Dennis O'Leary said they believe the fire was caused by the occupant of the house cooking and leaving it unattended.
It is understood one person was in the house at the time. O'Leary said the damage was extensive.