Gas leak kills 3 in Milan
The girls aged 7 and 11 were taken to hospital, local media reported. Their mother and a couple who lived in the building were killed. Another person was also injured in the blast.
A host of ambulances and fire engines were dispatched to the scene in Giulio Carcano Street.
The explosion happened early in the morning, when most residents were at home.
Rescuers are searching the rubble for other potential victims.