Amnesty International has called for the release of three labour activists held after conducting an investigation into conditions at factories making shoes for Ivanka Trump’s label and other Western brands.

The New York-based China Labour Watch said Hua Haifeng was detained by mainland police after he attempted to travel to Hong Kong last week to release the findings of the group’s undercover probe. Two of his colleagues, Li Zhao and Su Heng, are also missing and they too are believed to have been detained.

Their investigation had been into labour practices at factories that produced footwear for US President Donald Trump’s daughter Ivanka Trump and other Western brands such as Nine West, Karl Lagerfeld and Coach.

“Hua Haifeng, Li Zhao and Su Heng must be released if they are being held solely for investigating possible labour abuses at factories making shoes for Ivanka Trump’s label,” said William Nee, China researcher at Amnesty International.

“Activists exposing potential human rights abuses deserve protection not persecution from the authorities,” Mr Nee said, adding that the three researchers were the latest to fall foul of an aggressive campaign by Chinese authorities against activists who have any ties to overseas organisations, citing “national security”.

The incident is the latest controversy over Ms Trump’s activities in China. Last month, her company won approval from the Chinese government for three new trademarks on jewellery, bags and spa services on the same day she and her husband dined with President Xi Jinping at Mar-a-Lago.

Under Mr Xi’s government, there has been a crackdown on civil society, focused on human rights activists, lawyers and press freedom.

China Labour Watch is one of the highest profile rights groups working in China, examining working conditions in factories that were the backbone of China’s massive economic expansion, supplying some of the world’s top companies. Over the years the group has singled out major foreign firms for censure over how the workforce in their suppliers have been treated. Mr Li said the group’s work had in 17 years never attracted this kind of scrutiny from state security.

Mr Hua was arrested in Jiangxi province on suspicion of illegally using eavesdropping equipment, said Li Qiang, executive director of China Labour Watch.

The focus of the investigation was Huajian Group, which Mr Li said had violated labour codes on overtime, minimum wage, verbal abuse of workers and violations of womens’ rights.

“For years, Ivanka Trump has ignored public reports of awful labour conditions at a factory that makes her shoes,” Adrienne Watson, a spokeswoman for the Democratic National Committee, said in a statement.

“Now, she must decide whether she can ignore the Chinese government’s apparent attempt to silence an investigation into those worker abuses. Ivanka’s brand should immediately cease its work with this supplier, and the Trump administration should reverse its current course and confront China on its human rights abuses,” Ms Watson said.

(Additional reporting agencies)