Police personnel stop commuters and ask valid reason to come out during lockdown in New Delhi, India, March 24, 2020. The number of confirmed COVID-19 cases in India Tuesday rose to 492, India's health ministry said. (Xinhua/Partha Sarkar)

India, the world's second most populous country, may have a large number of unreported COVID-19 infections, as more than 1.3 billion people undergo three weeks of unprecedented lockdown from today, Chinese analysts said on Wednesday. 

When the nationwide lockdown came, India had only reported 519 confirmed COVID-19 cases as of press time. 

India's leader may have imposed a nationwide lockdown because he is aware of the seriousness of the outbreak, as it is a very strong measure and could slow down its economy and impact every aspect of people's lives, Zhao Gancheng, a research fellow at the Shanghai Institute for International Studies, told the Global Times on Wednesday. 

But the number of confirmed cases released by the Indian government only stands at 519, which means India may have a large number of patients who haven't been officially reported, Zhao said. 

Normally, the preventive measures adopted by the government should be consistent with the epidemic situation, otherwise imposing such a strong measure at this time would be unreasonable, Zhao said. 

India has found the virus spreading between communities and the actual infection number would be much larger than what has been reported, Xie Chao, an assistant professor on Indian studies at Tsinghua University, also told the Global Times on Wednesday.

Chinese observers have predicted in early March that the battle against the coronavirus infection in India may just be beginning, as thousands haven't been tested due to insufficient and cumbersome nucleic acid test criteria. 

The load of screening samples from suspected cases in India is limited as previously only a few national laboratories were authorized to conduct nucleic acid tests, which must be done at least twice before a confirmed case is reported and the testing duration is usually pretty long, an India-based observer told the Global Times previously.

The Indian Council of Medical Research had expanded its testing criteria on March 20. Contacts of confirmed Covid-19 patients and hospitalized patients with severe acute respiratory illness will be given a test. Those who have undertaken international travel in the last 14 days will also be tested if they show symptoms, the Indian institute said. 

But previously, the nucleic acid test was only given to people identified as "suspected cases" which must conform to a certain criterion, India's health ministry said. 

However, the Indian government has not altered its policy that only when samples are tested positive twice shall the case be categorized as a confirmed case. 

There are also Indian experts and media pointed out that the nation is one of the lowest rates of COVID-19 testing, with stringent protocols.

Only a few government designated places are able to confirm the tests. The National Institute of Virology based in Pune, one of them, only tests an average of 25 samples a day. But in China's Wuhan, a modernized lab with automation equipment can test 10,000 samples a day, according to chinanews.com.

The cumbersome testing criteria and long testing duration could mean a lot more people who might be infected with the COVID-19 are out there. If an epidemic happens in India, it could be a nightmare for the world, observers noted.