Shanghai has strengthened safety checks for vegetables at the World Expo park，the city's largest vegetable supplier said Monday.

"Besides the safety examination by vegetable producers, we have begun to conduct another round of safety checks to ensure vegetables sent to the world expo park are safe and fresh," said Chen Jun, director of the quality management office with the Shanghai Jiangqiao vegetable wholesale market, the sole vegetable supplier for the world expo park restaurants.

The 184-day World Expo, which is scheduled to open on May 1, is expected to receive 70 million visitors. Food supply has become a crucial issue for the city.

It's estimated expo visitors and staff will consume at least 200 tons of vegetables of 175 varieties every day. The market has contracted with 40 vegetable farms across China, said Chen.

"The vegetables are organic and pollution-free. Cauliflower, tomato, pepper, cabbage, potato and green leaf vegetables were most in demand during the trial operation of the world expo park and we have increased orders for them by 20 percent," he said.

In addition, a tracing system has also been built for the transfer of vegetables destined for the expo.

To ensure the safety and quality of the vegetables, eastern China's Shandong Province, which is responsible for about half of the vegetable supply for the expo, has required farmers to use the same vegetable seeds, fertilizer and breeding processes.

"The standards are the same level of strictness as those for the vegetables sent to the 2008 Beijing Olympic Games," said Wang Xiaojun, head of the Cangshan County government in Shandong.

Cangshan has been designated as a vegetable-producing base for the world expo, with 15 varieties of Cangshan vegetables, such as garlic, tomato and leek, chosen for supply to the world expo park.

"All the vegetables have been grown here for at least two years. We have also sent agricultural technicians to the farms to supervise the use of pesticides," Wang added.