Anthony D. Weiner’s mayoral campaign entered a dark and chaotic phase on Thursday as he admitted to having explicit online relationships with at least three women since he left Congress, and the woman at the center of the latest scandal appeared on television, remembering him as a “perpetually horny middle-aged man.”

Mr. Weiner, appearing shaken and at times rambling as he faced reporters, revised his previous estimate of the total number of women with whom he had engaged in sexual encounters online to 10, up from 6.

But in a sign of how difficult the furor over his behavior may be to contain, he made clear he could not say for certain how many women or lewd images might yet surface.

“There are more than — there are a few,” Mr. Weiner, a Democrat, said with a stammer. “I don’t have a specific number for you.” Later, he tried to explain the sequence of his Internet relationships: “Sometimes they didn’t go consistently. Whatever.”