CHONGQING, March 6 -- This 10,000-square-meter farm in southwest China's Chongqing Municipality may look ordinary at first glance. Yellow rapeseed, crops, greenery and a pond can be seen.

But this is no ordinary farm - it's actually situated on top of a factory that manufactures doors.

The farm is big enough that a tractor is needed to help with farming. The factory's staff grow crops there, as well as raise poultry and livestock. There's 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. After crops are harvested, they can take the vegetables and fruits they grow there home.

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

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

Lu said the building was built to code and is perfectly capable of holding 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.

But at the same time, city residents have also started paying more attention to improvements in life quality, 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 in addition to Chongqing.

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.