The curfew was imposed in several areas of Galle district yesterday night, police said.
A few houses and businesses belonging to the minority Muslim community has been attacked after a minor incident involving the majority Sinhala community.
Police's Special Task Force and the military has been deployed to bring the situation under control, police said.
About 19 people have been arrested, it said.
Muslims account for just 10 per cent of Sri Lanka's 21 million population. The community has been complaining of increasing attacks against them in recent years.
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