UPDATE 1-China's COVID-19 outbreak grows as cities race to trace infections

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BEIJING, Oct 20 (Reuters) - China reported a fourth day of new locally transmitted COVID-19 cases in a handful of cities across China, prompting alarmed local governments to double down on efforts to track potential carriers amid the country's zero-tolerance policy.

A total of 17 new local cases were reported for Oct. 19, up from nine a day earlier, data from the National Health Commission (NHC) showed on Wednesday.

The new cases were reported in eight cities and administrative divisions, more than four for Oct. 18, the bulk of which were in northern and northwestern China. Three separate cases were also reported in recent days in the south and southwest of China.

Among the cases was one in the capital city Beijing, which is busy gearing up for its hosting of the 2022 Winter Games in February, where officials vowed stringent efforts against the virus.

Almost half of the 26 local cases found on Monday and Tuesday were of close contacts of an elderly couple who had travelled in the provinces of Shaanxi and Gansu and the Chinese region of Inner Mongolia before being confirmed as COVID-19 patients on Sunday.

It remains unclear whether the married couple were the source of the outbreak, or where they had contracted the virus.

After the couple's travel history was disclosed, many cities scrambled to trace their close contacts, requiring people who had been to places where those with detected cases had travelled to report to local authorities and get tested.

The city of Jiayuguan in northwestern Gansu province even launched its second round of city-wide testing after an initial round yielded no positive results, following reports that some of those with cases recently visited the city.

Officials have not disclosed how those with cases reported on Monday and Tuesday contracted the virus, but tentative signs indicated there might be multiple sources of the virus across China, which could complicate the country's efforts to seek zero infections.

Three out of the five local cases found this week in Erenhot city, in Inner Mongolia, did not appear to have any connection with infected travellers in other cities, but were linked to a case detected on Oct. 13, a person who worked at a local logistics hub. It is unclear how this person was infected. (Reporting by Ryan Woo, Roxanne Liu, Stella Qiu and Liangping Gao Editing by Jacqueline Wong and Peter Graff)