HKMA has been intervening in exchange rate around 5 to 6 a.m - Bloomberg

The Hong Kong Monetary Authority (HKMA) has recently bought the local currency, the Hong Kong dollar (HKD) around 5 a.m. to 6 a.m., to keep it from the falling below the weak end of its trading band, according to Bloomberg.

The HKD has fallen to the lower end of its trading band at HK$7.85 repeatedly this month, courtesy of its interest rate discount to the USD. That has forced the HKMA to spend $1.5 billion to defend the exchange-rate peg, leading to an uptick in the interbank borrowing costs. 

Also, liquidity is thin during the gap between NY close and Asia open and so large orders have an abnormal impact on the exchange rate, which pushes the HKMA into action.