The Honk Kong Monetary Authority (HKMA) is HK's defacto central bank.
The HKD is pegged in a range and from time to time the HKMA intervenes in the market to maintain that range. Today the HKMA injected HKD 1.86bn following earlier 3.31bn.
As you can see in the chart below, the HKD has been at the strong end of its range since the beginning of April:
