Children's products sold by the Chinese-founded online shopping giant Shein contained toxic substances in amounts hundreds of times above acceptable levels, the government of South Korea's capital Seoul said Tuesday.

Shein, headquartered in Singapore, has skyrocketed in popularity around the world in recent years, offering a vast selection of trendy clothes and accessories at stunningly low prices.

This explosive growth has also led to increased scrutiny of its business practices and safety standards, including in the European Union and South Korea - where Seoul authorities have been conducting weekly inspections of items sold by platforms including Shein, Temu and AliExpress.

In the latest round, they selected eight products sold by Shein, including children's shoes, leather bags and a belt and found several to contain high amounts of phthalates - chemicals used to soften plastics.

One pair of shoes contained 428 times the permitted levels of phthalates - the highest observed so far during the Seoul inspections - and three bags had amounts as high as 153 times the limit, the city government said.

Phthalates are widely used to soften plastic and are found in thousands of products including containers, beauty products and toys. However, they have been known for decades to cause hormone disruptions and have been linked to obesity, heart disease, some cancers and fertility problems.

Seoul city official Park Sang-jin told AFP they had requested removal of these products from sale, and said that since the city began inspections in April, most platforms have complied with such requests.

A Shein spokesperson told AFP the company "takes product safety very seriously".

The company requires its suppliers to comply with its controls and standards, and works with international third-party testing agencies to ensure compliance with product safety standards, it said.

"Upon learning of any claim against our products, we immediately remove the product(s) from our site as a matter of caution whilst conducting our investigations," it said, adding it takes appropriate follow-up action "if non-compliance is verified".

So far, Seoul authorities said they have inspected 93 products and found that almost half of them contained toxic substances. These items include children's watches and colouring pencils.

Last month, the European Union added Shein to its list of digital firms that are big enough to come under stricter safety rules - including measures to protect customers from unsafe products, especially those that could be harmful to minors.

Shein and Temu have followed Chinese e-commerce titan Alibaba in challenging Amazon, especially by making inroads in the US market.