The head of Human Rights Watch has reportedly been barred from entering Hong Kong.

Immigration authorities told Kenneth Roth, the organisation's executive director, he could not enter the region after he arrived at the city's airport.

He was planning to launch a report in which the lead essay – written by Mr Roth himself – makes a case for how China is trying to undermine the international code on human rights, the advocacy group said.

“Even though I’ve been able to enter Hong Kong freely before,” the director said in a video from the airport, “this time – for the first time – they blocked me.”

The US citizen said he would fly back to New York to give the press conference on Human Rights Watch’s annual world report there instead.

Mr Roth added: “Sadly this episode is just the latest evidence that the Chinese government is doing everything it can to undermine the enforcement of international human rights standards.”

Human Rights Watch said authorities did not explain why its director was blocked from entering Hong Kong.

The move to bar Mr Roth follows China’s pledge last month to sanction organisations it claimed had “performed badly” in relation to anti-government protests taking place in Hong Kong.

Human Rights Watch, the National Endowment for Democracy, and Freedom House - all US-based organisations advocate for rights - were all mentioned by Beijing.

Protests in Hong Kong were sparked over seven months ago by a proposed bill allowing extradition to mainland China, and have since evolved to encompass wider pro-democracy and anti-government sentiment.

Demonstrators' five demands include universal suffrage and an independent investigation into alleged police brutality.

Over one thousand people gathered in the semi-autonomous region over the weekend to urge people and governments abroad to support the city’s pro-democracy movement and oppose China’s ruling Communist Party.