China has tightened security along its southwestern border to try to stop a spillover in coronavirus cases from Vietnam . To keep infections at bay, authorities in the region of Guangxi have cracked down on illegal entry, detained smugglers helping illegal border-crossers, set up extra checkpoints along the border and launched mass testing for residents. The city of Pingxiang added 51 checkpoints to the 96 it already had and started 24-hour security patrols along its 97km (60 mile) border with Vietnam, local media reported. The city also quarantined and detained two people on Sunday for transporting illegal border-crossers, some of whom tested positive for the coronavirus, the reports said, quoting a notice issued by the local command centre for Covid-19 control. “[Their acts] seriously threatened the economic development, social stability and people’s health and lives in … our city,” the notice said. Guangxi reported seven imported infections and four asymptomatic cases on Friday, all in Pingxiang. China has maintained tight border controls and strict quarantine measures to prevent imported coronavirus infections. Chinese citizens who plan to return to the country via land border crossings are required to take a Covid-19 test within 72 hours of entry, according to the Chinese embassy in Vietnam. Vietnam reported more than 15,000 infections and 256 deaths on Thursday. The average number of deaths reported each day has risen 10 days in a row. On Monday, the Guangxi Centre for Disease Control and Prevention said one person who legally entered the country tested positive for the virus and had been isolated in the regional capital of Nanning. It said another person who took a bus from Nanning to the southeastern province of Fujian had also been quarantined after testing positive. The National Health Commission reported 37 new local symptomatic cases on Friday, with 24 in the northern Chinese border city of Manzhouli in Inner Mongolia . Other infections were detected in two cities in eastern Zhejiang province, Dehong Dai and Jingpo autonomous prefecture in southwestern Yunnan province, Harbin in northeastern Heilongjiang province and Xian in northwestern Shaanxi province. In addition, 23 asymptomatic cases were found in Zhejiang, and 46 new imported cases were detected, of which 26 were symptomatic. As of Thursday afternoon, Zhejiang had reported 59 cases in three cities, including Shaoxing where some cases were found to be linked to a funeral. The province has suspended group tours and travel packages to other provinces and limited the number of visitors to tourist attractions and facilities such as theatres, libraries and museums to 75 per cent of their maximum capacity. Vice-Premier Sun Chunlan said on Tuesday that the key to coronavirus control was to guard the gates to the country and prevent imported cases. “Covid-19 control during the new year and Spring Festival is important for a successful Beijing Winter Olympics and safety during the festive seasons,” Sun said. “[We should] accelerate the vaccination drive, especially for the elderly who are at high risk.”