The Ministry of Education denied on Tuesday that math questions for the postgraduate studies entrance exam had been leaked online.

Netizens raised the alarm when it appeared that several questions shown by a teacher during video recordings of a training course were similar to those on the math test, with only some figures having been changed.

The incident was the hottest topic on Sina Weibo on Tuesday, generating millions of comments and forwards.

More than 2 million people registered for this year’s postgraduate exams, which took place over the weekend.

The ministry said it launched an investigation immediately after reports of the leak and ordered exam center to check the video footage, screenshots and PDF materials.

The authority said experts confirmed that the questions in the videos were different from those in the postgraduate math test.

An official with the ministry’s exam center said any interference in the national exam would be dealt with seriously.

Four videos, each lasting about 40 minutes, show teacher Li Lin giving a lecture on advanced math to students in a classroom with the logo for training website Zhongshikaoyan.

According to an introduction on the website, Li is a veteran educator who helps prepare students for the postgraduate exam. He also teaches at Dalian University of Technology.

I’ve been giving math lectures for postgraduate entrance exams since 2005, Li said on Sina Weibo. "Although the Ministry of Education and the university have issued regulations prohibiting such activities, I still took my chance to give lectures without permission.

I’m so sorry for the negative effect this has had on the university, he said.

Li’s videos have been deleted from the training website.

China’s postgraduate exams have been plagued by scandals in recent years. In December 2016, a man in Jiangsu province was caught selling the answer sheets, causing an uproar.