BEIJING, Oct. 21 (Xinhua) -- An increasing number of postgraduate students is triggering concerns over the education quality in Chinese universities.

According to the Ministry of Education, about 517,000 postgraduate students were enrolled in 2012, over 220,000 more than in 2003.

Postgraduate students in some leading Chinese universities have outnumbered undergraduates, according to the latest research report issued by Wuhan University, based in central China's Hubei Province.

At Tsinghua University, one of China's most elite universities, the ratio between the undergraduate and postgraduate students currently stands at 0.61 to 1, said the report quoted by Sunday's Wuhan Evening News, a local daily.

In the country's top ten universities, including Tsinghua University and Peking University, students graduating from postgraduate programs last year outnumbered those finishing undergraduate programs, the report said.

For instance, the number of students that graduated from postgraduate programs in 2011 was about 2,500 more than that for undergraduate programs at Peking University, and the figure stood at 2,800 at Renmin University of China, the report said.

Moreover, Wuhan University had 7,704 postgraduate vacancies and 7,650 undergraduate vacancies this year.

The increase in postgraduate students has posed great challenges to faculty. According to the report, 15.7 percent of university professors are supervising more than ten postgraduate students each, and 1 percent of them are supervising more than 20 students each.

The appropriate number of postgraduate students for one professor is three and the maximum is six, or the professor will not be able to control the quality of his or her work, said Qiu Junping, director of the Research Center for Chinese Science Evaluation under Wuhan University, which issued the research paper.

The sharp increase in vacancies for postgraduate programs is believed to help hold some of undergraduate students back from entering the tough employment market, but some universities also see it as a source of revenue.

According to a report on the employment of college students in 2009 and 2010, issued by the Ministry of Education, the employment rate of postgraduates was lower than that of undergraduates in the two years.

"Chinese universities are hoping to improve their research capabilities, but this does not depend on the number of postgraduates," Qiu said.

The most urgent issue is controlling the number of postgraduate students and improving the quality of education, he added.