How do local labour markets shape the employment effects of minimum wages? We evaluate this question using comprehensive manufacturing firm data and over 28,000 hand-collected county-level minimum wages during China's market transition (1998-2007). We find that, consistently with monopsony models, the employment response to higher minimum-wage exposure becomes less negative as local employer concentration increases, with positive point estimates arising in highly concentrated markets in some specifications, particularly among domestic private firms. Higher minimum-wage exposure may also be associated with lower reported training expenditure and greater firm exit. Our findings indicate that the employment effects of minimum wages can depend critically on local market structures, highlighting the importance of geographical and institutional heterogeneity when assessing labour regulation in transitioning economies.