A Fire and Emergency NZ spokesperson said the fire was reported about 9am on Wednesday.
Two engines were sent to the block of flats after smoke was seen coming from an upstairs unit.
"There is a fire at the address, though the entire house is not on fire," the spokesperson told chrislynchmedia.com.
"We received quite a few calls, so it was obviously putting up a bit of smoke, which is quite visible in Christchurch this morning."
Hato Hone St John transported two people in moderate condition to Christchurch Hospital.
A New Zealand Herald photographer described the scene. He said he saw flames coming from the flat when he arrived.
"The homeowners are very emotional. I can see one woman being treated for burns and a baby also being assessed by ambulance," the Herald photographer said.
Crews from the Christchurch City and Woolston stations were sent to the scene and managed to contain the fire to the upstairs area.
Fenz staff were investigating the cause of the blaze and police were also at the scene.
It comes after two businesses were badly damaged by a fire in an industrial building on Maces Rd, Bromley, on Monday. The blaze sent thick black smoke across the city.
Earlier that day a controlled burn-off also caused smoke to drift across the city. Fenz said the burn-off next to Bottle Lake Forest Park had been affected by the weather conditions on Monday morning and residents noticed more smoke than usual.
