Thames Valley Police said they were called alongside firefighters to the blaze in the city’s Erleigh Road, which broke out about 1.30am.
There have been “multiple casualties”, some of whom have been seriously injured. A family is being supported after the “large” fire, said police.
The blaze has since been extinguished.
Thames Valley Supt Zahid Aziz said: “Unfortunately as a result of this fire, several people have been injured, and some of these are serious.
“The fire was contained at a single property, and no adjoining properties have been affected.
“The family affected by this fire will be offered support, and we have commenced a joint investigation with Royal Berkshire Fire & Rescue Service and our officers will remain at the scene for some time to come.”
A spokesperson for the fire service said: “There were some serious injuries to the occupants who are now being treated in hospital. Firefighters have been on the scene overnight and a fire engine will likely remain on the scene for some time.”
Pictures from the scene appear to show the fire being contained to one home with adjoining properties not affected.
Eight ambulances, a hazard area response team and the air ambulance were deployed to the scene.
