China's revised legislation designed to expand the scope of activities that amount to espionage takes effect on Saturday.

The law first took effect in 2014 to enforce a crackdown on spying. The government of President Xi Jinping approved the changes in April.

There are concerns among the international community about the legislation being implemented arbitrarily due to the vague definition of what amounts to espionage.

On top of stealing state secrets and information, the definition of spying activities now includes theft of documents, data, reference materials and items related to national security and interests.

Japanese government officials say Chinese authorities have detained at least 17 Japanese nationals for alleged spying since 2014.

Nine were sentenced and served prison terms. The trials were held behind closed doors, and Chinese authorities did not elaborate on how they had breached the law.

Eleven have returned to Japan after being released or completing their terms. One died of illness in prison. Five are still being detained or serving time in prison.

In May, China's counterintelligence authorities reportedly investigated an international consulting firm based locally and in the United States for allegedly acquiring state data illegally.

The revised legislation raises concerns about a wider crackdown on foreign nationals and firms in China.