Nearly half of China's chemical plants pose "major environmental risks", China's State Environmental Protection Administration (SEPA) has said.
Chemical leaks are not uncommon in China
SEPA warned of an increase in pollution incidents if safety was not improved, the official Xinhua news agency said.
Gas or chemical leaks blamed on poor construction or maintenance are not uncommon in China.
The report comes days after a chlorine gas leak left 160 people in hospital in the north-western city of Yinchuan.
Forty-five percent of the country's chemical and petro-chemical plants posed "major environmental risks", SEPA said.
Out of 7,555 facilities surveyed across China, 81% were located along rivers and lakes or in densely-populated areas, the environment agency said.
If "effective measures" were not taken, "the trend of surging environmental incidents in the country would not be checked", the agency warned.
Sunday's leak of chlorine gas was blamed on a break in a rusty pipe, Xinhua news agency said.
Tonnes of carcinogens were released after the Jilin blast
The victims of the toxic fumes were said to be mainly children and elderly people who lived nearby.
The leak was under control by Monday, Xinhua said.
In March, some 15,000 residents were forced to evacuate their homes after a leak from a gas well in the south-west of the country.
Pollution risks have risen up the political agenda since a major incident in November.
An explosion at a chemical factory in the north-eastern province of Jilin resulted in the release of 100 tonnes of the carcinogens benzene and nitrobenzene into the Songhua River.
The chemicals moved hundreds of kilometres downstream. Water supplies had to be cut in the town of Harbin, leaving some of its 3.8 million people without water for five days.
In January, Chinese environment chief Zhou Shengxian said the government's priorities were changing:
"The Chinese government has made a very timely and determined decision to stop the conventional approach of development, which could be characterised as 'pollution and destruction first, treatment later'," he told a news conference.