The T2K experiment observes indications of νμ→νe appearance in data accumulated with 1.43×1020 protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with |Δm223|=2.4×10−3  eV2, sin22θ23=1 and sin22θ13=0, the expected number of such events is 1.5±0.3(syst). Under this hypothesis, the probability to observe six or more candidate events is 7×10−3, equivalent to 2.5σ significance. At 90% C.L., the data are consistent with 0.03(0.04)<0.28(0.34) for δCP=0 and a normal (inverted) hierarchy.