Shopping mall operator Guangdong Highsun Group Co was questioned by the Shenzhen Stock Exchange earlier on Thursday (13 June) after this week announcing it was backing development of an African swine fever vaccine.

Beijing strictly regulates research on, and handling of, the virus.

Highsun said on Tuesday it would spend 900 million yuan ($130.09 million), or 26 percent of its 2018 net assets, on supporting research into a natural compound it said had been shown to prevent the disease which is deadly to pigs and ravaging herds across Asia.

But the ministry said it had not received a research application and without experimental data, the claim that a polysaccharide injection is effective in preventing the virus lacked scientific proof.

Researchers around the world have been trying for years to develop a vaccine against African swine fever without success.

Highsun said that preliminary research had found the polysaccharide to be 92 percent effective in preventing the disease in clinical trials - an announcement which triggered a 10 percent surge in its shares on Wednesday, leading to a trading suspension.

The Shenzhen exchange said it was seeking clarity on several issues, including additional data regarding the vaccine's effectiveness and whether the researchers had government approval to conduct research on the virus.

An official from Highsun, who asked not to be identified, said the company was preparing a response to the exchange's questions and declined to comment further.

African swine fever kills almost all the pigs it infects. The breeding herd in China, the world's top pork producer, has declined by a record 24 percent owing to the disease, the agriculture ministry said on Thursday.

The Bureau of Agriculture and Rural Affairs for Hainan province said on its website on Thursday that it had supported a research team that had isolated a polysaccharide compound from tropical plants which had shown a "certain preventive effect" against African swine fever.

However, it said more research was needed in areas including the possible impact of virus mutation and the safety, stability and feasibility of industrial production of the compound.

It is not clear if the bureau was referring to the same team backed by Highsun and it did not answer calls for a comment on the statement.

Highsun's shares rose 7.3 percent to 3.38 yuan ($0.49) a share after resuming trading on Thursday.

($1 = 6.9185 Chinese yuan renminbi)