The Hong Kong Monetary Authority (HKMA) raised the base rate charged through its overnight discount window by 25 basis points on Thursday to 2.25 percent after the U.S Federal Reserve raised interest rates by a quarter of a percentage point. Hong Kong tracks U.S. rate moves because its currency is pegged to the US dollar. The Hong Kong dollar has repeatedly hit the lower end of its trading band in April and May. The HKMA had mopped up a total HK$70.35 billion of Hong Kong dollars from the foreign exchange market since April 12, nudging up a key lending rate that could push borrowing costs higher. The HKMA, the city's de facto central bank, sets its base rate through a formula that is 50 basis points above the prevailing U.S. Fed Funds Target or the average of the five-day moving averages of the overnight and one-month HIBORs (Hong Kong Inter-bank Offered Rate). In March, the HKMA raised the base rate by 25 basis points to 2.00 percent and the central bank's chief warned that mortgage rates in one of the world's most expensive property markets would have to rise in the longer term. However, major banks such as HSBC and Standard Chartered have left the city's lending rate unchanged. Hong Kong's record-breaking private home prices rose at their fastest pace in a year in April, the latest government data showed, as the city's hot housing market showed no sign of cooling. The financial hub has one of the least affordable housing markets in the world, with flat prices doubling between 2010 and 2017.