A woman was killed Thursday morning in a house fire in Fairhaven, the state fire marshal’s office said. The fire started at 10:26 a.m. in the kitchen of the home at 304 Mill Road, Jennifer Meith, spokeswoman for the fire marshal, said in a statement. Authorities did not identify the victim. “We couldn’t really see anything other than a hose going up to the garage apartment,’’ said neighbor Sandra Fleurent. “We could smell and see smoke.’’ The fire is believed to have been accidental, but is still under investigation, Meith said.