Law & Order cast members have included, from left, S. Epatha Merkerson, Jerry Orbach, Dianne Wiest, Jesse L. Martin, Angie Harmon and Sam Waterston. (Reuters)

Venerable TV drama Law & Order is about to close the courtroom doors.

NBC announced Friday that the original version show would end May 24, after a run of 20 years.

Law & Order was on the verge of becoming the longest-running drama in prime-time television history, surpassing Gunsmoke, but it will have to settle for a tie with the 1960s western.

NBC also said Friday that it had renewed Law & Order: Special Victims Unit, and is adding a spinoff: Law & Order: Los Angeles.

Shot on location in New York, the drama followed the cops and lawyers of the U.S. criminal process.

Created by Dick Wolf, it has had a revolving door of stars, including Jeremy Sisto and Anthony Anderson as detectives and Linus Roache, Sam Waterston and Alana de la Garza as district attorneys.

In the past few years, the series seemed to be suffering creative fatigue and its ratings had fallen.

On Thursday, when cast and crew were informed about the cancellation, rumours began to leak about the end of the series.

Wolf was reported to be in negotiations overnight in an attempt to save the series, but had to settle for the spinoffs.

NBC's full 2010-11 schedule will be officially released Sunday.

Director Marisol Torres, right, is seen with recent Law & Order cast members, from left, S. Epatha Merkerson, Jeremy Sisto and Anthony Anderson. (Bernadette Tuazon/Associated Press) With files from The Associated Press