An Astellas Pharma employee who was detained by Chinese authorities on espionage charges fell out of contact on the day he was set to leave for Japan, according to sources familiar with the matter.

The Japanese businessman in his 50s has roughly 20 years of experience working in China for the Japanese pharmaceutical company, the sources said.

A Chinese foreign ministry spokesperson revealed on Monday that the businessman is being questioned on suspicion of violating China's criminal and anti-espionage laws.

The employee was due to return to Japan in March, as he was reassigned to a different post. But on his scheduled day of departure, officials lost contact with the man after he left a hotel.

This is the latest in a string of cases in which Japanese nationals have been detained on spy charges since 2014, when the anti-espionage law came into force in China. It was unclear what activities constitute espionage, since trials have been held behind closed doors.

Officials say the latest case has rattled Japanese communities in China. They are worried that it could have a significant impact on the economic relations between the countries.