"We're concerned about pollution in general," Graziano da Silva, director-general of the FAO said.
"We have seen a lot of improvements in China but there is much more to be done," he was quoted as saying by state-run Xinhua news agency.
In May, three rice mills in central China's Hunan Province were investigated after rice was found to be contaminated with cadmium, a carcinogenic industrial chemical.
A food safety inspection showed that 44.4 per cent of rice and rice products in the city of Guangzhou in south China's Guangdong Province also contained excessive amounts of cadmium, according to a Guangzhou Food and Drug Administration statement on May 16.
Although the source of the pollutants has not yet been found, heavy metal contained in fertilisers has contaminated irrigation water and arable land.
Agricultural authorities in Hunan said in 2012 that heavy metal pollution has been spreading from urban agricultural production bases to rural areas, he sadi.
"It's not exactly true that the more fertilizers you use, the more output you get," the FAO chief said.
China produced about 6.21 million tonnes of fertiliser in 2011, accounting for about 20 per cent of global output, National Bureau of Statistics (NBS) data showed.
China, as the world's largest fertilizer user, consumed about 30 percent of total global output annually.
But its effective utilisation rate of pesticides is still lower than that of developed countries, with a 10 to 20 percentage points gap, according to the NBS statistics.
Overuse of fertiliser will increase soil's dependency on pesticides, said Pan Genxing, an agricultural expert with the Nanjing Agricultural University.
"Soil contamination and food safety problems are inevitable and are bound to occur in high-growth countries," Merritt Cluff, an FAO economist he told Xinhua noting that land and water resources per person was a problem in China.
"China is unique in the respect that land and water scarcity make difficult combinations. Some other countries may have experienced a similar period, but they did not have such high growth pressure," Cluff said.
In order to address these issues, Graziano da Silva and Cluff advised the Chinese government to invest in order to achieve high productivity.
The government should be strict in controlling the use of pesticides and fertilizers, da Silva said.
"There is also the issue of consumers rejecting food products that are not up to standard," he said.