China is battling its highest number of coronavirus infections since the beginning of the pandemic. The number of officially reported cases remains minuscule, compared with that of many countries. But with top leaders touting a “covid zero” approach, local officials are under intense pressure to halt the spread before the Winter Olympics begin in Beijing next month. On Sunday, the city of Tianjin near the capital began mass testing of all its 14 million residents after two cases of the omicron variant were detected, according to state media. Residents stood in long lines bundled up against the cold to take the tests.