(Refiles to additional clients; no change in text.) SHANGHAI, March 16 (Reuters) - At least one major state-owned Chinese bank is conducting large currency swaps in mainland markets, possibly as part of efforts to cap the yuan, as domestic banks deal with a heavy influx of dollars, eight sources with knowledge of the matter told Reuters on Tuesday. The sources said the bank was seen conducting sell-buy swaps in the dollar-yuan pair, alongside its purchases of dollars from exporters and other corporate clients. They suspected the swaps were aimed at getting around monthly quotas on the amount of foreign currency banks can buy, by transferring some of those dollar purchases onto their forward books. “The big bank has been buying quite huge amounts of one-year dollars in the swap market,” said one source, speaking on condition of anonymity. Another source said other banks had also been using swaps to disperse their dollar buying into the future. The trades have pushed one-year dollar/yuan swap points to 1,750 points, from lows of around 1,610 last week. One-year yuan has dropped to 6.68 per dollar, from around 6.63 a week ago. As China recovered rapidly from the coronavirus pandemic and saw exports boom, it recorded a huge trade surplus of $535.03 billion last year, the highest since 2015. That, analysts said, was the reason for a rush among corporations to convert their dollars into yuan, before it appreciates further. The currency is up almost 5% since the end of September 2020. China’s FX reserves have, however, barely moved in the past few years, staying just above the $3 trillion mark. Economists and analysts said the People’s Bank of China’s net foreign-exchange purchases have stayed steady in recent months, suggesting commercial banks might not have swapped the dollars they acquired from their corporate clients with the central bank. Instead, these dollars flowed to the interbank market. “It’s possible that the foreign exchange from corporates has been transferred to the swap market, and it would not appear in data,” said Ken Cheung, chief Asian FX strategist at Mizuho Bank in Hong Kong.