New rules that tighten Chinese government restrictions on the country’s internet companies have come into effect today, raising concerns about how they will be applied.

The expanded State Secrets Law compels firms – including social media giants Tencent, ByteDance and Weibo – to take action if users post sensitive information.

It requires “network operators” to monitor information being shared by users. The rules also describe how posts should be removed, records saved and reported to authorities.

This is the law’s first update in more than a decade and is in line with President Xi Jinping’s focus on national security as the government cracks down on China’s vast technology industry.

When the new rules were first announced in February, a National Administration of State Secrets Protection official told the state news agency Xinhua that they were necessary as “the guarding of state secrets faces new problems and challenges in the new era”.

While internet companies in China are already subject to strict rules, the changes “set a new standard for active self-monitoring and rapid cooperation”, said Hong Kong-based law professor, Ryan Mitchell.

The revised rules also broaden the definition of what may be deemed as sensitive information to include “work secrets”, or information about the decision-making of state agencies, which could be particularly problematic for journalists, including foreign correspondents.

“A main concern for us is the uncertainty as to what really constitutes a ‘state secret’,” Jens Eskelund, President of the European Union Chamber of Commerce in China told the BBC.

“Clear demarcations and definitions would be helpful,” he added.

Taiwan has also voiced concerns about the new rules and said they could place visitors from the island to China at risk.

Taipei’s Mainland Affairs Council said the legislation is “highly vague and may cause people to break the law at any time”.

The international law firm Baker McKenzie FenXun said that while the definition of what are considered to be state secrets is “broad and vague” it should not have a substantial impact on multi-national companies operating in China.

The new regulations come as the social media giant TikTok, and its Chinese parent company ByteDance, are facing increased scrutiny in the US and other Western countries.

However, the new rules “do not seem to be mainly geared towards regulating the overseas operations of Chinese firms”, Mr Mitchell said.