Six Marxist students vanish in China in the lead up to Labor Day

Paramilitary police officers march in Tiananmen Square after a ceremony marking the centennial of the May Fourth Movement on April 30.

Beijing (CNN)Six Marxist university students who wanted to spend International Labor Day working alongside regular laborers have vanished in China, the latest in a series of disappearances and detentions of student activists.

An activist group linked to the six missing students announced their disappearance in a statement released Tuesday. CNN tried to reach out to the students but found their phones were switched off.
Since August 2018, left-wing students, including those from Beijing's prestigious Peking University, have been detained across China apparently over their involvement in worker protests in different parts of the country.
    The Chinese government is highly sensitive to attempts to organize protests or support what it considers subversive messages. In most countries, International Labor Day is often marked by parades and demonstrations held by trade unions, but in China is generally regarded as a holiday, despite the country's Marxist roots.
    The latest round of disappearances appear to have taken place in recent days, ahead of a speech Tuesday by President Xi Jinping in honor of the 100th anniversary of the May 4 student protests.
    Former president of the Peking University Marxist Society, Qiu Zhanxuan, announced on social media Sunday he planned to head to a well-known job market on the outskirts of Beijing, where thousands of migrant workers gather daily to find odd jobs.
    Qiu Shanxuan, president of the Peking University Marxist Society, on December 17 in a photo published by the Jasic Workers Support Group.
    Workers in China are supposed to have several days off during International Labor Day holiday, and Qiu said he intended to work alongside average laborers during this period, adding he didn't believe his plan would be well received by the government.
    "If doing this kind of manual labor makes me disappear, everyone knows who did it," he wrote on his social media.
    On Sunday, while walking with four other students, Qiu posted pictures of six men who he said were plainclothes police officers following the group. Then the public posts stopped. The next day, an activist group associated with Qiu announced the five members were missing.
    CNN called Qiu and another of the missing student's numbers, but both phones were switched off. It isn't the first time Qiu has been disappeared. In December, he was bundled into a car by suspected plainclothes police officers.
    Qiu and his group weren't the only Peking University students to vanish in the past week either. On Sunday evening, student Shen Yuxuan sent messages to a friend saying she was being harassed by a group of policemen and security guards on campus. Shen was also associated with Qiu's Marxist Society.
    She hid in a bathroom, according to messages seen by CNN, but