The fire broke out on Monday evening at approximately 4 am at Laburnum Avenue, Hornchurch in Essex.
Twenty-one firefighters and four fire engines were on the scene.
Two men, aged 74 and 76 were taken to hospital to be treated for their injuries but passed away earlier today.
One woman, aged 68, was pronounced dead at the scene.
The two deceased males are believed to be brothers and the deceased woman a wife of one of the males.
Minister for Foreign Affairs, Charlie Flanagan, expressed his sympathies and The Department of Foreign Affairs are providing consular assistance to the families involved.
The cause of the fire is not yet known.