NEW DELHI—New Delhi imposed a weeklong lockdown on April 19 to prevent the collapse of the Indian capital’s health system, which authorities said had been pushed to its limit amid an explosive surge in coronavirus cases. In scenes familiar from surges elsewhere, ambulances catapulted from one hospital to another, trying to find an empty bed over the weekend, while patients lined up outside medical facilities waiting to be let in. Ambulances also idled outside of crematoriums, carrying half a dozen dead bodies each. “People keep arriving, in an almost collapsing situation,” said Dr. Suresh Kumar, who heads Lok Nayak Jai Prakash Narayan Hospital, one of New Delhi’s largest hospitals for treating COVID-19 patients. Most of them desperately need oxygen, Kumar said. But the city is facing shortages of oxygen and some medicine, according to Chief Minister Arvind Kejriwal, who told reporters that the new stringent measures being imposed were required …