SHANGHAI—At least six people were injured in a knife attack Tuesday, in the third stabbing at a Chinese train station since March and the latest challenge to President Xi Jinping's increasingly blunt anticrime rhetoric.

Police said before midday a single man slashed people outside a downtown railway station in the southern Chinese city of Guangzhou. An armed police officer fired at and wounded the attacker, police said, helping authorities capture the perpetrator with help from others.

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