A gas burner for cookers of the type fitted to a cooking hob includes a central body having a first flame distribution ring and at least one external body, fluidly separated from the central body and substantially concentric with it, having at least one second flame distribution ring. In addition, structure is provided for separately feeding the mixture of primary air and gas to the central body and to the external body. This structure includes at least one horizontal mixing chamber with a radial Venturi effect.