HONG KONG—China Evergrande Group shares slumped to a record low on Monday as authorities intervened to reassure markets after the heavily-indebted property developer warned on a coupon payment, pushing it closer to default. China’s central bank said it would cut reserve requirements for banks while the politburo vowed to promote healthy development of the property sector, reinforcing previous messages to investors that Evergrande’s woes could be contained. Having made three 11th-hour coupon payments in the past two months, Evergrande again on Monday faced the end of a 30-day grace period, with dues totalling $82.5 million. Its shares tumbled by 20 percent following a statement on Friday that creditors had demanded $260 million and that it could not guarantee funds for coupon repayment, prompting the regime to summon its chairman. As at the end of Asia business hours, two bondholders said they had yet to receive payments from Evergrande. Evergrande declined …