The Honk Kong Monetary Authority (HKMA) is HK's defacto central baank.
The HKD is pegged in a range and from time to time the HKMA intervenes in the market to maintain that range.
Just in - HKMA increased its injection to HKD 4.65bn.
As you can see in the chart below, the HKD has been at the strong end of its range since the beginning of April:
HKMA 'inject' funds to try to weaken the HKD from the boundary.
