Students in 21 primary and middle schools in East China's Shanghai were ordered to stop wearing their uniforms on Monday after a toxic dye was found in the products of a local garment firm.

In a recent quality inspection campaign, aromatic amine dye, which can cause cancer, was detected in one batch of student uniforms produced in July 2012 by the Shanghai Ouxia garment company, said the Shanghai Municipal Bureau of Quality and Technical Supervision.

Six batches of the company's clothes products were substandard, said the city's quality watchdog. The company has been one of a number of producers of school uniforms in Shanghai for five years.

Education authorities in the Pudong New Area of Shanghai said in a statement they have demanded the 21 schools who had purchased uniforms from Ouxia to tell students to stop wearing the clothes, which require quality examinations.

The company, which has stopped production, sold 15,000 school uniforms annually.

It is common for students to wear uniforms in Chinese primary and middle schools.