HONG KONG, April 4 (Reuters) - Hong Kong's de-facto central bank bought HK$7.104 billion ($905.22 million) worth of U.S. dollars in the open market during New York trading hours to stop the local currency weakening beyond its target range.

The Hong Kong dollar is pegged within a band of 7.75 to 7.85 versus the U.S. dollar. It touched 7.85 on Monday.

The aggregate balance - the main gauge of cash in Hong Kong's banking system - will fall to HK$69.915 billion on April 6, an HKMA spokesperson said on Tuesday morning. ($1 = 7.8478 Hong Kong dollars) (Reporting by Donny Kwok; Editing by Christopher Cushing)