Hong Kong on Saturday began enforcing a mandatory two-week quarantine for anyone arriving from mainland China, a dramatic escalation of its bid to stop the deadly new coronavirus from spreading.The vast majority of people crossing the border are expected to self-quarantine and will face daily phone calls and spot checks by officials, with up to six months in prison for those found in breach of the isolation period.Authorities hope the prospect of quarantine will virtually halt cross-border traffic while allowing the city to remain stocked with food and goods from the mainland, where the virus has now killed more than 700 people.Arrivals have plummeted by 75% in recent weeks. But thousands queued in neighbouring Shenzhen on Friday night to beat the midnight deadline before the new quarantine rules came in.By early Saturday morning only a trickle of people were arriving via the Shenzhen Bay crossing."I have to come back because my daughter is going to school here," a woman who gave her surname as Song told AFP after ending a 20-day family holiday on the mainland."We will quarantine ourselves, because this is for the public good," she added.A security guard who gave his surname as Lam said arrivals were up about 50% in the last few days and most were Hong Kongers.Cabinet ministers unveiled how the quarantine would work on Friday evening, just six hours before the new policy took effect.Hong Kong residents are allowed to self-quarantine at home and mainland and international visitors at hotels or other accommodation they have arranged.But those with no planned accommodation will be taken to temporary facilities prepared by the government.Anyone who has been to mainland China in the past 14 days and then flies into Hong Kong from another destination will also be quarantined.Visitors with a visa for less than 14 days will be denied entry, which will block most mainland visitors, who tend to travel to Hong Kong on a seven-day permit.The city is planning to use an army of volunteers from the civil service and some students to make spot checks and daily calls to ensure people are staying at home.Panic-buyingThe new regulations have been enacted under a sweeping emergency law that allows the city's leaders to bypass the legislature during an outbreak of disease.Exemptions are being made for a variety of key jobs including flight and shipping crews and cross-border truck drivers to ensure goods and food keep coming into the city.Hong Kong gained first-hand experience of a deadly disease outbreak in 2002-03 when Severe Acute Respiratory Syndrome, or SARS, swept through, killing 299 people. The virus left profound psychological scars and saddled people with a distrust of authorities in Beijing who initially covered up the outbreak.In the last week the city has been hit by a wave of panic-buying, with supermarket shelves emptied of staple goods such as toilet paper, hand sanitiser and rice.The government has said supplies are stable and false online rumours were behind the frenzy.More than 3 000 people have now been infected with the new coronavirus across China.Hong Kong has 26 confirmed cases, with one patient who died earlier this week.Many of the newer infections have no history of travel to mainland China, prompting fears the city now has a self-sustaining outbreak.There have been growing calls for the mainland border to be sealed entirely. But Hong Kong's pro-Beijing leadership, which has record-low approval ratings after months of pro-democracy protests, has been reluctant to make such a move.They have however gradually shut all but two of the land borders while keeping the airport open.