An envelope with an unknown white powder was sent to Manhattan’s elite Spence School Monday morning — just days after other schools received similar suspicious packages.

Police said the substance was found at the celebrity-loved, all-girls school at 74 E. 91st St. on the Upper East Side Monday morning.

The school was out for spring break and no students were in the building, cops said.

Police were still on scene investigating Monday afternoon.

Last week, the NYPD put out information on how to spot suspicious packages after responding to five schools that received similar mail.