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SmS, a prototypical intermediate valence compound as well as a candidate material for correlated topological insulator, has been studied by performing high-pressure nuclear magnetic resonance measurements on a $^{33}$S-enriched sample. The observation of an additional signal below 15-20~K above a nonmagnetic-magnetic transition pressure $P_{rm c2} = 2.0$~GPa gives evidence for the magnetic transition. The absence of a Curie-term in the Knight shift near $P_{rm c2}$ indicates that the transition occurs in electronic states where the localized character of $4f$ electrons is screened through a substantial hybridization. Two distinguishable signals coexist during the stepwise evolution of magnetic volume fraction with lowering temperature near $P_{rm c2}$, which is well described in the regime of first-order transition. The fact that hyperfine fields from the ordered moments cancel out at the S site leads us to a conclusion that the ordered phase has the type II antiferromagnetic structure.
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