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.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.