A government investigation has been launched to probe the disappearance of about 700 foreign students who have stopped attending classes, and have been out of contact since last April, because some no longer hold valid visas, a university in Tokyo has said.

Tokyo University of Social Welfare had 5,133 foreign nationals enrolled as of May 1, the second-largest foreign student body after Waseda University’s 5,412, according to the Japan Student Services Organization.

But the private university attended by some 8,000 total students in total said last week it had lost touch with about 700 of the roughly 2,600 foreigners who had attended the university’s Oji campus in Kita Ward, Tokyo. The students were enrolled as researchers for the current academic year, which ends later this month.

The students include nationals from Vietnam, Nepal, China and other countries, and have been removed from the university’s student register, according to its public relations office in Nagoya.

The university said it also recorded 264 such disappearances in 2016 and 493 in 2017. In many cases, students went missing after attending classes several times and later stopped paying tuition.

The school, established in 2000 in Isesaki, Gunma Prefecture, has four campuses, in Tokyo, Isesaki and Nagoya.

In 2017, the Justice Ministry said dozens of foreign students registered with the university were found to be illegally staying in Japan even after their visas had expired.