Shenzhen police have relaxed some measures they brought in recently to regulate the number of electric bikes and tricycles in the city.

It is an attempt to ease the impact on the express delivery sector of a crackdown launched on March 21.

Under the crackdown, anyone operating an electric bike or tricycle in the city - a private individual or delivery company-needs a license.

The change announced on Tuesday provides 5,000 new licenses for delivery drivers, an increase from the 13,000 licenses that were previously available for them.

The delivery industry will also benefit from a 15-day transition period, during which companies can buy replacements - such as new-energy freight cars that do not require a license.

The delivery industry has been booming in Shenzhen. In 2015, the average person sent and received a total of 129 packages - an increase of more than 40 percent over 2014, according to the Shenzhen Municipal Postal Administration.

Liu Xiaoding, head of the transport police command department, said the crackdown on electric bikes and tricycles was necessary because of a growing safety problem. Liu said city authorities received more than 1,500 complaints relating to electric vehicles last year-65 percent of transportation complaints. Accidents involving electric bikes and tricycles led to the deaths of 114 people - 26.4 percent of the total death toll in transportation incidents.

He said the next step will be to target manufacturers, retailers and repair shops involved in supplying substandard electric bikes and tricycles.

The Shenzhen police department said its crackdown on electric bikes and tricycles is not aimed at the delivery industry but mainly at substandard vehicles being used as illegal taxis.

Between March 21 and April 5, police impounded 18,000 electric bikes and tricycles in Shenzhen because they were unlicensed or not roadworthy.