BEIJING, Dec. 31 -- Zhang Shuai has only taken one day off in the past two months. Every day he has been running around a residential quarter in eastern Beijing to make sure packages from around the country are delivered intact and on time.

Zhang, 23, is one of the country's hundreds of thousands of delivery men who just helped set a record in the booming e-commerce industry. According to figures from the State Post Bureau, some 540 million parcels and boxes were delivered in six days from Nov. 11 to 16 for Singles' Day, China's biggest online shopping holiday.

No matter where a package comes from, most are delivered by people like Zhang in the last mile before they reach their destinations. Zhang rides an electric tricycle fully loaded with parcels from a distribution center to the block where he works, hustling from one floor to another to deliver them.

Delivery companies need men like Zhang, especially at the end of the year, when online shoppers place online orders for the holiday season.

Young, diligent and ambitious to trade their labor for more income, they don't care about the freezing Beijing winter and demanding customers. Zhang does not have special windproof clothes to protect him as he rides, just a woolen hat and warm trousers.

As a newcomer to the business, he did not know that delivery workers are susceptible to stomach diseases and arthritis. "I know health is the foundation for making money, but sometimes I just don't have the time to attend to myself."

Apart from the Spring Festival and Christmas, e-commerce giants Alibaba and JD.com have also made Nov. 11 (Singles' Day) and Dec. 12 into online shopping extravaganzas. Alibaba smashed its online sales record this year, reaching 57.1 billion yuan (9.33 billion U.S. dollars) in Singles' Day sales on Taobao.

For days after the Singles' Day shopping craze, Zhang only ate instant noodles because he was so busy.

It is easy to find job postings for delivery companies claiming workers can earn as much as 10,000 yuan per month, much higher than what an assembly line worker can earn.

Zhang earns less, with a monthly salary of 3,000 to 4,000 yuan, because the block where he works is sparsely populated and the order flow is not very high.

"I don't doubt that the job is very promising, because even old ladies in this quarter know about online shopping. What would they do without us?"

Zhang delivers an average of 100-plus packages daily, which isn't too demanding. Yet he still has to be careful.

YTO Express, Zhang's employer and one of China's largest delivery companies, requires early delivery packages to be delivered before 2 o' clock p.m. If there are late deliveries, Zhang will be fined 100 yuan, almost his daily wages. And if he loses a package, he needs to pay the full price.

To keep customers happy, the company also launched night delivery services, which require delivery men to work after 7 o'clock in the evening.

A branch manager of YTO Express surnamed Zhang (not related) said that delivery jobs have become the first choice for migrant workers looking to work in Beijing.

To retain workers, many delivery companies now provide accommodation and meals. "Two years ago, we only got scooters. Now we have more delivery trucks and electric tricycles, but the turnover remains high," said the manager.

Zhang Shuai plans to contract for a delivery service in the future and work on his own. "It is much more profitable to open a new service center and employ others to make deliveries, but before that, I need to make enough money for the investment."