A crackdown on the use of unlicensed electric bikes and freight tricycles in Shenzhen, Guangdong province, has paralyzed courier services, leaving delivery workers struggling to cope with piles of undelivered packages.

The campaign, launched by the city's traffic police on March 21, has resulted in the seizure of 17,975 electric bikes by March 31, and 874 people were detained on charges of operating them illegally, according to the police's Sina Weibo account.

Only electric bicycles that have been registered with the traffic police are allowed to operate on the roads and freight tricycles have been forbidden in the city.

The campaign has hit Shenzhen's express delivery sector hardest, because most of the couriers use electric freight tricycles to deliver packages.

Ling Chuang, a 27-year-old manager of a service outlet operated by Shanghai Yunda Express, said the ban on electric bikes and tricycles means workers are now only able to process about 50 percent of orders.

None of the electric bicycles used by Ling's outlet has been registered with the traffic police, and using e-bikes to deliver packages is far less efficient than using tricycles, he said.

The police have said they will continue the crackdown, but on Friday they offered a 15-day buffer period. "Anybody using an electric tricycle against regulations will face administrative detention, without exception, starting from April 16," according to a police statement issued on Thursday.

Ling said it would be impossible for couriers to use trucks to deliver the orders because they have to move from community to community and make regular stops.

In response to widespread complaints from delivery workers, the police said the move was designed to make roads safer. They will help to reduce the shortfall by licensing an additional 5,000 electric bikes for the courier sector, but Ling said the number would still fall short of demand.

About 4 million package orders are processed in Shenzhen every year, but there are more than 70,000 delivery workers and only 13,000 licensed e-bikes.

The crackdown has also affected Ling's earnings because failure to deliver orders on time results in financial penalties levied by the company.

"We are also receiving a greater number of customer complaints about delays, but right now we really don't have a solution ourselves and no solution has been offered to us," he said.

The campaign has also resulted in the detention of nearly 50 couriers and the seizure of 800 electric tricycles, according to local media.

"To me, it is not worth putting yourself behind bars for just trying to do your job," Ling said, adding that he is considering quitting the sector.

Zhao Kangjun, a 33-year-old delivery worker with ZTO Express, said the official crackdown has left him tired and even scared at times.

"I have to work an extra four to five hours every day to deliver all the packages," he said. He now works from 9 am to 11 pm, and has started using a pedal-powered three-wheeled bike in preference to his electric tricycle.

The penalties imposed for delayed deliveries are also a concern. A fine of 50 to 100 yuan ($7.70-$15.40) is imposed for every day the goods are delayed, and Zhao said he usually pays 500 to 1,000 yuan in fines every month, even when he uses an electric tricycle.

The increase in the workload has already forced some workers to abandon the sector. Zhao said his service outlet, in the Longhua district, used to employ about 30 couriers, but about one-fourth has left the company since the campaign started.

The crackdown has also resulted in some couriers reducing the number of packages and orders they will accept.

Huang Wei, 35, a company executive in Shenzhen, said she was stunned when a courier refused to accept her order and told her that his company has no alternatives to electric vehicles.

"He said he was too scared to go outside. I thought it was an April Fools' joke," Huang said.

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