Former Vice President Joseph R. Biden Jr. said at a fund-raiser in New York on Monday night that he had already amassed 360,000 donors with an average contribution of $55 — a disclosure that appeared to reveal he has raised $19.8 million for his presidential bid.

That is more than any other candidate raised in the first quarter of the year, when Senator Bernie Sanders paced the Democratic field and raised $18.2 million from more than 500,000 donors, and there are still two weeks remaining in the second quarter for Mr. Biden.

The revelation came at an unusual moment.

Campaigns typically guard their financial hauls closely, only releasing figures at strategic moments to maximize their impact. Mr. Biden made the declaration at the Upper East Side home of the hedge fund manager Jim Chanos.