Hong Kong’s stock market is suffering from a post-holiday hangover. The flood of Chinese money into the city before the mainland’s National Day celebrations in early October has slowed to a trickle since traders returned from the week-long break. Investors in Shanghai spent more than $8 billion on Hong Kong shares in September, the biggest monthly inflow via the exchange link since it began in 2014. Net buying this month through last week was just 7 percent of that amount, data compiled by Bloomberg show. The narrowing valuation discount on the city’s dual-listed shares and concern about the Federal Reserve’s impending rate increase may have spurred mainland investors to turn off the taps, according to Hong Kong analysts, who also say they’re perplexed at the speed of the shift. The change is a headwind for equities after the influx of Chinese money helped drive the Hang Seng Index up 12 percent last quarter for its best such gain in seven years. “It’s a bit of a mystery as to why this is happening,” said Mohammed Apabhai, head of Asia trading strategy at Citigroup Inc. “Nobody has put forward a convincing explanation about exactly why the southbound flow has dried up and whether it’s a temporary phenomenon. That has removed one of the supports from the Hong Kong equity market.” China International Capital Corp Ltd. cut its rating on Hong Kong-listed mainland banks last week, citing the dwindling inflows. Trades from Shanghai made up as much as 17 percent of the total turnover in Hong Kong at one point last month, the highest on record, data compiled by Bloomberg show. That ratio dropped to less than 7 percent on Oct. 20. The exchange link, started about two years ago, opened up a channel for Chinese individual investors to buy Hong Kong stocks, while giving foreign investors more access to mainland shares. “This surprised a lot of people,” said Ronald Wan, chief executive of Partners Capital International Ltd. in Hong Kong. “People thought a lot of funds will be channeled from the north. The flow will come back eventually if third quarter figures demonstrates genuine improvement in the Chinese economy and whether that converts to earnings as well.” The slowdown in southbound flow is just a temporary phenomenon, according to Fan Cheuk Wan, Hong Kong-based head of Asia investment strategy at HSBC Private Bank. Interest will pick up again and lend support to the Hong Kong market as mainland investors continue to look for ways to diversify their assets amid a weakening yuan, she said. China’s onshore currency slid 0.1 percent to 6.7743 per dollar on Monday, extending a six-year low. So far, the flow hasn’t picked up. Net buying totaled 275 million yuan ($41 million) on Oct. 20, according to exchange data compiled by Bloomberg. Hong Kong’s market was shut Friday because of a typhoon. Mainland investors purchased about 700 million yuan of the city’s stocks on Monday, as the Hang Seng Index reversed early losses to rise 1 percent. For Uwe Parpart, Hong Kong-based chief strategist at investment bank Capital Link, the outlook isn’t bright for the city’s equities. Mainland A shares offer better opportunities than stocks in Hong Kong, which is facing headwinds from a possible December interest-rate hike by the Federal Reserve, he said. With Hong Kong’s currency pegged to the dollar, its borrowing costs track US rates. “I’m sure that people are seeing that, and realizing that right now it’s probably better to keep their money at home than sending it abroad,” Parpart said. It’s not only volumes that have changed, with mainland investors shifting their attention to a different group of Hong Kong stocks as well. Some of the names that saw the biggest inflows in September, mostly financials such as HSBC Holdings Plc, Industrial & Commercial Bank of China Ltd. and China Construction Bank Corp., have been sold heavily or have disappeared from the top-traded stocks this month.