China is reportedly curbing exports of black clothes from the mainland to Hong Kong in an effort to hamper anti-government protests which have rocked the global financial hub for more than four months.

Protesters have adopted plain black tops, jeans, trainers and face masks as their defacto uniform during rallies that began in opposition to a controversial extradition bill but have now snowballed into wider demands for democratic rights.

According to the South China Morning Post, a notice published on September 26 by the EXPRESS courier service in Guangdong, a coastal province close to Hong Kong, contained a long list of items that could not be delivered to the special administrative region.

Among the banned items are black shirts and other clothing, helmets, umbrellas, walkie-talkies, drones, goggles, metal chains, safety vests and torches.

In July, another notice by Guangdong courier company PHXBUY put a halt on similar goods, including flags, flagpoles and banners.

Yellow helmets, face masks and plastic eye goggles have become key equipment during the demonstrations as protesters seek to protect themselves from tear gas and rubber bullets fired by riot police. Umbrellas have been used as shields against dyed water being shot from cannons.

Couriers have warned that “customers mailing products have to use their real names” and that “thorough investigation” will be launched if any of the forbidden items are discovered.