Hong Kong’s de facto central bank stepped in for the first time since August 2014 to prevent the city’s currency from rising against the U.S. dollar as a surge in stocks drove up demand.

The Hong Kong Monetary Authority said it bought $400 million on Thursday at HK$7.75 a dollar, the upper limit of a convertibility range that triggers intervention. The purchase, disclosed on the authority’s Bloomberg page, was confirmed by the HKMA.

“Demand for the Hong Kong dollar increased alongside the rise in the stock market recently,” the monetary authority said in an e-mailed statement, adding that it would continue to closely monitor “market developments.”

Hong Kong’s 32-year-old peg came under pressure as the city’s benchmark Hang Seng Index jumped to a seven-year high on Thursday. Money from a mainland exchange link is contributing to record turnover in the city’s $4.9 trillion stock market, as investors twice used up their daily quota for purchasing Hong Kong equities.

The Hong Kong dollar was little changed at 7.7503 versus the greenback as of 11:27 a.m. in the city Friday, according to data complied by Bloomberg. The currency on Wednesday touched 7.75 for the first time since January. The Hang Seng Index was steady, heading for its biggest weekly advance since 2011.

Chinese Capital

Chinese investors bought 10.5 billion yuan ($1.7 billion) of Hong Kong shares - the maximum allowed -- on both Wednesday and Thursday. They acted after the Chinese regulators late last month announced that more fund managers could buy equities listed in the city.

“The HKMA will likely have to inject again as capital keeps flowing into Hong Kong’s stock market,” Kenix Lai, a Hong Kong-based currency strategist at Bank of East Asia Ltd., said by phone on Thursday. “The Hong Kong dollar will trade near the strong end of the trading range in the near term. It isn’t due to speculation on the peg but massive capital inflows.”

Hong Kong pegged its currency to the U.S. dollar in 1983 when negotiations between China and the U.K. over the city’s return to Chinese rule spurred capital outflows. In 2005, policy makers committed to limiting the currency’s decline to HK$7.85 per dollar and capping gains at HK$7.75.

The Hong Kong Monetary Authority injected a total of $9.7 billion into the financial system to defend the peg in July and August last year, according to data compiled by Bloomberg.