HONG KONG, Sept 23 (Reuters) - The Hong Kong Monetary Authority (HKMA) sold HK$961 million ($124 million) in New York trading hours after its local currency hit the strong end of its trading band, according to data released by the HKMA.

The aggregate balance - the key gauge of cash in the banking system - will increase to HK$242.49 billion on Sept. 24, an HKMA spokesman said early on Wednesday.

The Hong Kong dollar is pegged in a narrow range of 7.75-7.85 to the U.S. dollar. The HKMA has been conducting sales in recent sessions to weaken the currency to keep it within that trading band.

($1 = 7.7496 Hong Kong dollars) (Reporting by Donny Kwok; Editing by Tom Hogue)