Thousands of protesting students held a school principal hostage over fears their degrees would be devalued, Chinese police said on Tuesday.<br />'' <br />''The protests were over a plan to merge a Nanjing college in Jiangsu province with a vocational institute – which are seen as less prestigious.<br />'' <br />''Such protests are rare in China where mass movements are controlled.<br />'' <br />''<span style="color: #222222;">A video on Twitter showed thousands of chanting undergraduates surrounded by officers outside, as police chased after them and dragged individuals out of the crowd.</span><br />