A leaky kitchen gas hose was blamed Sunday for an apartment building explosion that threw residents against walls, blew out their windows and hurled debris into the streets.

The explosion Saturday injured more than 20 people, including four badly burned girls.

Fire marshals believe natural gas leaked from a flexible hose connection behind a stove in a first-floor apartment, said Tony Sclafani, a fire department spokesman.

Local utility Consolidated Edison earlier said investigators checked pipes going from the street to gas meters and apartments and found all of them to be working properly.

The burned children were in critical condition at New York Presbyterian Hospital-Weill Cornell Medical Center.

The mother of the four girls, ages 1 to 5, was also in critical condition, said John Rogers, a hospital spokesman.

The building has been shored up, but residents will not be allowed in until it is deemed safe for occupancy, said Robin Brooks, spokeswoman for the city's Department of Buildings.