By Shilpa Jamkhandikar and Neha Arora

India's western state of Maharashtra is training thousands of health workers in how to care for children afflicted with COVID-19 as a first line of defence against surges involving new variants, health officials and experts said on Tuesday.

The state, home to the financial capital of Mumbai, was the worst hit by a devastating second wave of infections in April and May that killed hundreds of thousands, and is still reporting a quarter of all new cases nationwide.

It has re-imposed curbs to rein in the fast-spreading Delta variant that has touched off new outbreaks globally, even as daily national tallies stand at their lowest in nearly two months, allowing some states to re-open businesses.

"We are training thousands of health workers, who are usually the first point of contact for families, on how to deal with COVID care in children," Suhas Prabhu, head of the state's pediatric task force, told Reuters.

While there is no data showing children are more vulnerable, a government survey in Mumbai from April to mid-June showed the presence of virus antibodies in at least half of those younger than 18.

"The experts are indicating that a sizeable number of children are likely to be infected in the third wave," said government adviser Dr Subhash Salunke.

Paediatric critical care remained a 'weak link' in the health system, the former World Health Organization official told Reuters.

India, which is using AstraZeneca's domestically produced Covishield doses and the home-grown Covaxin, has yet to approve any vaccines for children.

Maharashtra, with a population of more than 114 million, is one of the country's most populous states, and has reported 50 cases of the new Delta Plus variant that India has designated as being of concern.

It is an offshoot of the highly infectious Delta variant that caused a spike in cases in April and May which overwhelmed healthcare facilities, swamping crematoriums.

From 400,000 cases a day in May, daily new infections now stand at 37,566, health ministry data showed on Tuesday.

The South Asian nation's tally stands at 30.31 million, with a death toll of 397,637.