Thousands of children have been told not to wear their school uniform when the new term starts in Shanghai after samples tested by the city were found to contain carcinogenic chemicals.

More than 20 schools in the city have ordered the ban after six out of 22 batches of uniforms checked by the Shanghai Bureau of Quality and Technical Supervision failed tests for toxins and quality.

The uniforms, produced by Ouxia Clothing Co Ltd in Pudong, were found to contain banned dyes which could cause cancer, the bureau said on its official micro blog.

School uniforms on display at Ouxia Clothing Co Ltd in Shanghai on Feb 17. [Photo/Xinhua]

It also revealed the factory had appeared on a blacklist for quality for the past three years due to unqualified instructions or having a high pH index, which can lead to skin allergies.

An investigation is underway and the uniforms have been seized.

In 2012, a survey found more than half of school uniforms in Shanghai of poor quality, the lowest rate since 2007. City regulations allow any factory to produce school uniforms if they have orders, the quality bureau said.

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