BEIJING, Oct 19 (Reuters) - China reported nine new domestically transmitted COVID-19 cases on Oct. 18, the highest daily tally since the end of September, with the latest outbreak prompting two northern border areas to enforce a lockdown. Under a national policy of zero tolerance of domestic coronavirus clusters, cities with new infections have quickly tracked down and tested contacts of infections and sealed off higher-risk areas. Five of the nine new local cases were found in the northwestern city of Xian in Shaanxi province, and two were in the northern Chinese region of Inner Mongolia, data from the National Health Commission (NHC) showed on Tuesday. Erenhot city in Inner Mongolia, which shares a border with Mongolia, advised its 76,000 residents on Monday not to leave their residential compounds except when necessary. As of Tuesday morning, it had reported four local cases since Oct. 13. Travel in or out of the city is banned, except for essential cars with official clearance, the Erenhot health authority said. Ejina Banner, an administrative division in another part of Inner Mongolia, has closed all entrance and exit channels, launched a testing scheme on its 36,000 population and suspended school, local authorities said. Ejina had found five new local cases as of Tuesday morning in the latest outbreak. All were in close contact with two patients found in Xian on Oct. 17, the local authority said. Xian city has shut some tourist sites for disinfection, and those arriving from outside Shaanxi province must show proof of negative test results within 48 hours before they can visit tourist sites or stay at hotels. The southern city of Changsha in Hunan province and northwestern Yinchuan in the Ningxia autonomous region also reported one case each for Oct. 18, the NHC data showed. Yinchuan has advised residents not to leave town for unnecessary trips, and closed public venues such as bars and cinemas in two districts with higher virus risk. China"s capital, Beijing, reported its first local case since August on Tuesday -- someone who was on the same train as the infected person in Yinchuan. China had 25 coronavirus cases on Oct. 18, including infected travellers who arrived from abroad. China also detected 19 new asymptomatic patients for Oct. 18, which it classifies separately from confirmed cases.