Fifty student activists have gone missing in southern China after police raided an apartment where they had been mobilising support for factory workers demanding union rights.

Labour activists who were in touch with the group said the raid took place at 5am on Friday in Huizhou, near Shenzhen, in Guangdong province. Activists said they were not able to contact or locate those who had been detained. Video footage of the raid showed police in riot gear storming an apartment and scuffling with occupants.

The group, made up 50 students and five workers, is part of a small but growing labour rights coalition in China’s manufacturing region where independent labour unions are barred and activism is seen as a threat.

Another video recoding how the whole supporting group was taken away at 5am today! What a shame! Free all workers and students who fight for a unionizing right! pic.twitter.com/vtPTC9HIR2 — SACOM (@SACOM_HK) August 24, 2018

Last month, workers and their supporters staged protests at an industrial welding equipment factory in Shenzhen, Jasic Technology, in response to the firing of employees who had attempted to form a truly representative trade union within the country’s legal framework. All unions in China must register with the All-China Federation of Trade Unions, a government-affiliated group that usually sides with factory management.

The protests gained the support of Chinese university students who posted letters of support online, while others travelled to Shenzhen. The group of supporters has expanded to include retired party officials and Maoist groups. As of the end of July, 30 people had been arrested, according to Amnesty International.

Earlier this month about 50 students protested outside a police station in Shenzhen where workers and their supporters had been detained, according to China Labour Bulletin, a labour rights group in Hong Kong.

The group said two workers representatives and a student who had been advocating for the Jasic case had also disappeared.

On Thursday the group in Huizhou posted a video explaining their support for the workers. Standing in a group, wearing matching T-shirts, one said: “The reason the Jasic case has gotten so big is because [the authorities] refuse to deal with the problems themselves and insist instead on dealing with those who raise the problems.”