China introduced transit curbs for South Korean and Japanese nationals on Wednesday, in an escalating diplomatic spat over COVID-19 curbs that is marring the grand re-opening of the world's second-largest economy after three years of isolation.  China removed quarantine mandates for inbound travelers on Sunday, one of the last vestiges of the world's strictest regime of COVID restrictions, which Beijing abruptly began dismantling in early December after historic protests.  But worries over the scale and impact of the outbreak in China, where the virus is spreading unchecked, have prompted more than a dozen countries to demand negative COVID test results from people arriving from China.  Among them, South Korea and Japan have also limited flights and require tests on arrival, with passengers showing up as positive being sent to quarantine. In South Korea, quarantine is at the traveler's own cost.  In response, the Chinese embassies in Seoul and Tokyo said on Tuesday they had suspended issuing short-term visas for travelers to China, with the foreign ministry slamming the testing requirements as "discriminatory."  That prompted an official protest from Japan to China, while South Korean foreign minister Park Jin said that Seoul's decision was based on scientific evidence, not discriminatory and that China's countermeasures were "deeply regrettable."  In a sign of escalating tensions on Wednesday, China's immigration authority suspended its transit visa exemptions for South Koreans and Japanese.  The spat may affect economic relations between the three neighbors as well.  Japanese department store operator Isetan Mitsukoshi Holdings Ltd and supermarket operator Aeon Co said they may have to rethink personnel transfers to China depending on how long the suspension lasts.  "We won't be able to make short-term business trips, but such trips had dwindled during COVID anyway, so we don't expect an immediate impact. But if the situation lasts long, there will be an effect," said a South Korean chip industry source who declined to be identified, as the person was not authorized to speak to media.  China requires negative test results from visitors from all countries.  Counting deaths  Some of the governments that announced curbs on travelers from China cited concerns over Beijing's data transparency.  The World Health Organization has said China was underreporting deaths.  China's health authorities have been reporting five or fewer deaths a day over the past month, numbers that are inconsistent with the long queues seen at funeral homes. In a first, they did not report COVID fatalities data on Tuesday.  China's Center for Disease Control and Prevention and the National Health Commission did not immediately respond to requests for comment.  Without mentioning whether daily reporting had been discontinued, Liang Wannian, head of a COVID expert panel under the national health authority, told reporters deaths can only be accurately counted after the pandemic is over.  China should ultimately determine death figures by looking at excess mortality, Wang Guiqiang, the head of the infectious diseases department at Peking University First Hospital said at the same news conference.  Although international health experts have predicted at least one million COVID-related deaths this year, China has reported just over 5,000 since the pandemic began, a fraction of what other countries have reported as they reopened.  China says it has been transparent with its data.  State media said the COVID wave was already past its peak in the provinces of Henan, Jiangsu, Zhejiang, Guangdong, Sichuan and Hainan, as well as in the large cities of Beijing and Chongqing - home to more than 500 million people combined.  'Insulting'  On Wednesday, Chinese state media devoted extensive coverage of what they called as "discriminatory" border rules in South Korea and Japan.  Nationalist tabloid Global Times defended Beijing's retaliation as a "direct and reasonable response to protect its own legitimate interests, particularly after some countries are continuing hyping up China's epidemic situation by putting travel restrictions for political manipulation."  Chinese social media anger mainly targeted South Korea, whose border measures are the strictest among the countries that announced new rules.  Videos circulating online showed special lanes coordinated by soldiers in uniform for arrivals from China at the airport, with travelers given yellow lanyards with QR codes for processing test results.  One user of China's Twitter-like Weibo said singling out Chinese travelers was "insulting" and akin to "people treated as criminals and paraded on the streets."  Annual spending by Chinese tourists abroad reached $250 billion before the pandemic, with South Korea and Japan among the top shopping destinations.  Repeated lockdowns have hammered China's $17 trillion economy. The World Bank estimated its 2022 growth slumped to 2.7%, its second-slowest pace since the mid-1970s after 2020.  It predicted a rebound to 4.3% for 2023, but that is 0.9 percentage points below its June forecast because of the severity of COVID disruptions and weakening external demand.