US democracy watchdog group Freedom House urged governments on Wednesday to impose penalties on Chinese officials and tighten broadcast regulations amid a "dramatic expansion" in Chinese efforts to influence media overseas, Reuters reports.

"When Chinese diplomats and security agents overstep their bounds and attempt to interfere with media reporting in other countries, the host government should vigorously protest," it said in a report, adding that such officials could also be expelled.

It also said the United States and other governments should support policies that require Chinese media to disclose spending on paid advertorials, ownership structures, and other economic ties to Chinese state actors.

In recent years, Chinese state media and private internet companies have invested heavily overseas, prompting concern from lawmakers and rights groups that Beijing could remotely curtail criticism and expand its sphere of influence.

"While some aspects of this effort are in line with traditional public diplomacy, many others are covert, coercive, and potentially corrupt," said Freedom House, which is mainly financed by the U.S. government.

China has previously denied the accusations and has in turn criticized foreign social media companies for curtailing the voices of people who are supportive of the Chinese government.

Twitter and Facebook said in August they had dismantled a network of accounts that appeared to be part of a state-backed coordinated effort to undermine the pro-democracy protests in Hong Kong.

Freedom House was among several U.S. NGOs sanctioned by China in December over what Beijing says are efforts to interfere in its internal affairs.

On Sunday the head of Human Rights Watch, another U.S. NGO hit by the sanctions, was barred from entering Hong Kong ahead of the release of its global report, which strongly criticised China. China says the NGOs are inciting criminal activity by supporting pro-democracy forces in Hong Kong.

Freedom House calls for expulsion of Chinese envoys meddling with media