US TV actor Stephen Collins has admitted to "inappropriate sexual contact" with young girls in several instances decades ago, in an interview and an essay.

"Forty years ago, I did something terribly wrong that I deeply regret," Collins wrote, in an advance excerpt of an essay posted online by People magazine.

Accusations against the 7th Heaven star surfaced after secret recordings of a 2012 marriage therapy session, in which the actor described sexual contact with three girls between the ages of 11 and 13, were published by internet gossip site TMZ in October.

The incidents occurred in 1973, 1982 and 1994, the actor wrote in the essay.

Police in New York and Los Angeles have opened investigations into possible charges.

The interview with TV journalist Katie Couric and essay for People magazine will be broadcast and released on newsstands on Friday.