The results come amid escalating tensions between Beijing and Washington, with U.S. President Donald Trump unveiling sweeping bans on U.S. transactions with the Chinese owners of messaging app WeChat and video-sharing app TikTok.

Pinduoduo's second quarter operating loss widened to 1.64 billion yuan ($236.87 million) from 1.49 billion yuan a year earlier as the cost of maintaining its cloud services and call centre operations during the COVID-19 pandemic rose.

Its 12-month gross merchandise volume (GMV), a measure of business growth, was 1.27 trillion yuan. Although that was up almost 10% from the end of the first quarter, it failed to meet some analysts' expectations.

Vice President David Liu told Reuters that given the impact of the pandemic, it was not "meaningful" to compare second quarter GMV growth with the first.

"In Q2 this year we observed consumers' spending to be more value conscious," he said. "Users tend to associate Pinduoduo as their go-to platform for great savings everyday, so we also tend to have less of a concentrated spike in GMV and user activity around shopping promotions."

China has largely emerged from coronavirus-induced lockdowns but demand is still picking up in many sectors.

Pinduoduo's stock, which has more than doubled this year driven by robust growth in numbers of monthly active users, was set for its worst day in nine months should the pre-trade losses be sustained during the trading session.

Liu said the company would continue to closely monitor the situation regarding the United States and was prepared to work with the relevant regulators there and in China to address any concerns.

"We are committed to continuing our efforts to provide a high degree of integrity in our accounting," he said.

UBS said Pinduoduo's Q2 GMV was below its expectations and the operating loss ratio of 5.9% was the lowest in over two years.

However, "active buyers of 683.2 million grew 41.4% year on year, beating UBS' estimate by 1.7%," the bank said in a report.

Revenue surged about 67% to 12.19 billion yuan ($1.76 billion) in the second quarter ended June 30.

($1 = 6.9131 Chinese yuan renminbi)

(Reporting by Nilanjana Basu and Akanksha Rana in Bengaluru and Sophie Yu in Beijing; Editing by Krishna Chandra Eluri, Kirsten Donovan)