The number of Covid-19 cases in India has been doubling every three weeks but the epidemic is not growing exponentially in the country and South Asia region, the World Health Organisation (WHO) has said.

“In South Asia, not just in India, but in Bangladesh and [...] Pakistan and other countries of South Asia with large dense populations, the disease has not exploded, but there is always the risk of that happening,” Dr Mike Ryan, WHO's top emergency expert, told a news conference, according to Reuters.

WHO epidemiologist Dr Maria van Kerkhove said PCR tests can show a person with mild infection being positive for fragments of the virus 2-3 weeks after the onset of symptoms and those with severe cases “for much longer”.

“But we don't know what that relates to in terms of infectiousness, if somebody can actually pass the virus,” she said.