NEW DELHI — Massive crowds of Hindus began arriving in the northern Indian city of Haridwar on Thursday for the largest religious pilgrimage on Earth, even as experts warned it could cause a surge in COVID-19 cases as the country grapples with a second wave. The months-long Kumbh Mela festival, one of the most important Hindu celebrations, typically takes place every 12 years and draws tens of millions of pilgrims to four rotating sites. This year, it takes place in Haridwar, in the foothills of the outer Himalayas in Uttarakhand state, where devotees attend prayers and wash their sins away in the sacred waters of the Ganges River. Devout Hindus believe that the river water turns into "amrita," or the nectar of immortality, on particular days. But this year, COVID-19 measures have seen the festival postponed and then scaled back. The traditional start date, called Makar Sankranti, was in January, but people were not authorized to take holy baths in the river until the government"s formal launch in April. Although authorities moved the start date and shortened the pilgrimage from three and a half months to just one month, many people have chosen to disregard the official guidelines, said Oommen Kurian, senior fellow and head of health initiative at the Observer Research Foundation in New Delhi. Hundreds of thousands of people have been flocking to Haridwar since Makar Sankranti in January anyway — congregating in close quarters for hours a day, sharing public facilities, and having meals together. Photos show people washing their faces and taking full body dips into the sacred waters, then attending evening prayers by the banks of the river, lighting candles, and making religious offerings. Thursday saw the first ceremonies and holy baths take place by the banks of the Ganges, with holy men carrying out prayer rituals, said festival officer Harbeer Singh. Religious flags were hoisted ahead of their arrival, marking the formal start of the celebrations. The city"s district magistrate and police officials prayed to the Ganges river for a successful Kumbh Mela. "This is a festival which people wait years for," said Pradeep Jha, president of Ganga Sabha, a Hindu organization that provides services like organizing festivals along the Ganges. "Those who have problems at home, in work, in their families, they all come to pray here to mother Ganga and she blesses them." Jha had attended the morning Kumbh Mela ceremony, he added. "Kumbh Mela is not only a religious pilgrimage, but also perhaps the largest mass gathering at one place," said the federal government"s Ministry of Health and Family Welfare in late January, in an advisory laying out Covid-19 measures for the festival. The ministry said it expects to see a million people on "a regular day" during the festival. But on "auspicious days," attendees may swell to 5 million, and there could be a "large surge of crowds congregating ... to take holy baths." Experts fear the massive gathering could spell trouble for India"s Covid-19 situation, which has deteriorated markedly in recent weeks. India saw its cases drop by nearly 90 percent from a high in September 2020 to February this year, with many heralding the country"s apparent success in controlling infections. But March saw cases rise rapidly, raising an alarm of a second wave. India recorded 72,330 new cases of the virus on Thursday and 459 new related deaths. That"s the highest single-day increase in cases since last October, and the biggest rise in deaths since December, according to a CNN tally of data from the Indian Ministry of Health. The country has now recorded more than 12 million cases and 162,000 deaths since the pandemic began, according to Johns Hopkins University. "The situation is becoming from bad to worse and is a serious cause for concern, said V K Paul, a member of Indian government think tank Niti Aayog, on Tuesday. The surge in cases is due to several possible factors, said Kurian. There is a rise in new variants, which health authorities are still investigating with genome sequencing. People are going out more, and taking fewer precautions. The public may be experiencing Covid fatigue, or simply letting their guard down due to the winter success. "Kumbh Mela districts have been lucky in the last two months," said Kurian — but "given the acceleration in the number of cases, and the flow of people expected in the next few weeks, there can be a certain surge in cases, even if (safety measures) are implemented strictly." Authorities have introduced a range of health and safety requirements to try to minimize the risk. At least 7,000 police personnel and 1,000 festival officers have been deployed to carry out coronavirus surveillance and maintain security during the festival, Singh said. Visitors must register online and provide a medical certificate confirming their health status, according to directives from the state and federal government. Attendees must observe social distancing and wear face masks, and handwashing stations will be set up in public areas. All visitors coming from states with surging infections — 12 in total — must provide negative Covid-19 test results starting April 1, according to the official guidelines. Checkpoints at railway stations, airports, and other large hubs will carry out random testing on people passing through. Attendees may also be checked for their negative test results at several entry points. "The current (guidelines) are relatively strict, and anything even stricter may not be implementable," said Kurian. But the risks still run high with so many congregating in such a small space, sharing the same river water. Photos from the Ganges show packed crowds, people pressed together with no space for social distancing. Dozens, if not hundreds, of holy men dip into the water together, with no protective masks in sight. Jha, the Ganga Sabha president, acknowledged the pandemic was a "huge catastrophe" that "we should all be vigilant of." "But our health is our own," he said. "We all need to take adequate precautions to protect ourselves from Covid. As much as we are religious, we are also practical, so I appeal to everyone to keep a safe distance." "That being said, this year is incredibly auspicious and a lot of people are also going through a hard time, so seeking the blessings of mother Ganga has become all the more meaningful to them this year," Jha added. "It is an incredible feeling to witness this." Vulnerable groups like the elderly and those with comorbidities have been urged to travel only in emergency or unavoidable circumstances, said the Uttarakhand government on Tuesday. Health care workers and those on the front lines during the Kumbh Mela will be vaccinated. India began its vaccination rollout in January, with the goal to administer 600 million shots (that"s 300 million people since the vaccines require two doses) by August. India is administering two vaccines: one developed by Oxford University-AstraZeneca, known as Covishield in the country; and Covaxin, India"s first homegrown coronavirus vaccine, developed jointly by Bharat Biotech and the government-run Indian Council of Medical Research. So far, the country has administered more than 61 million shots, with about 8.9 million people fully vaccinated. That"s still less than 1 percent of the country"s 1.3 billion population, according to Johns Hopkins University. There is also still some vaccine hesitancy in the country, which could be hampering the vaccination effort and exacerbating the current surge, said Kurian. "India needs to ensure that the high-risk population is vaccinated as soon as possible, possibly running campaigns in high burden districts," said Kurian. "I think at the national level, judging from the momentum, we will soon see the September 2020 peak level of cases," he added. "Daily deaths reaching four digits again will be a huge tragedy for the country, and needs to be avoided at any cost." — Courtesy CNN