Employees harvest the vegetables and fruits they plant in the rooftop farm atop their factory at lunch break. CHEN CHENG / XINHUA

This 10,000-square-meter farm in Southwest China's Chongqing may look ordinary at first glance, with its yellow rapeseed, crops, greenery and a pond.

But this is no ordinary farm - it sits atop a factory that manufactures doors.

The farm is big enough that a tractor is needed to help with farming. The factory's employees grow crops there, as well as raise poultry and livestock. There are even a few peacocks roaming around the farm.

Factory official Lu Xiaoqing explained the company's rationale for setting it up. "It would be a waste if we left the big rooftop unused. That's why we created a farming project that involves our staff," he said.

Employees volunteer to take care of different parts of the farm. They can take the vegetables and fruits they grow there home.

One employee, surnamed Hu, is spending her lunch break harvesting spinach, asparagus and lettuce.

"Everyone is happy to do some farm work when they have free time. Now we can make full use of the rooftop and get vegetables for free. It's great," Hu said.

Lu said the building was built to code and is perfectly capable of supporting the weight of the farm. The roof has been waterproofed to prevent any possible leaks.

Urban land resources have continued to shrink in Chongqing due to expanding urbanization. The amount of land that can be used to plant gardens and trees has become increasingly limited.

At the same time, city residents have started paying more attention to quality-of-life improvements, which has given rise to the idea of rooftop greening.

Greening the rooftops of city buildings, or maintaining "living roofs," consists of partially or completely covering the roof of a building with vegetation planted over a waterproof membrane. Such efforts have been seen in other cities as well.

The Beijing Rooftop Landscaping Association said the gross area of green rooftops in Beijing had reached up to 1.2 million square meters as of 2012.

Xinhua in Chongqing