The Off Broadway revival of “Angels in America” is already a hot ticket, with a six-week extension announced soon after tickets went on sale.

The Signature Theater Company production — with a cast including Zachary Quinto, Christian Borle and Zoe Kazan — began selling ducats Tuesday morning, with the immediate high demand sparking the extension. The length of the additional run is unusually long among Off Broadway nonprofits, which often line up incremental extensions of one or two weeks at a time.

Initial interest is likely spurred both by the high profile of “Angels” among legit fans — as well as TV viewers, thanks to the Emmy-winning HBO adaptation — plus the fact that subsidized tickets costing $20 were available for the show’s initial run Sept. 14-Dec. 19.

Perfs that occur during the extension, which runs Dec. 21-Jan. 30, have a price tag of $85.

Bill Heck, Frank Wood, Billy Porter, Robin Bartlett and Robin Weigert round out the cast of the revival of the two-part Tony Kushner epic. Michael Greif helms.

“Angels” is part of the Signature’s 2010-11 season showcasing Kushner’s work, with a lineup that includes a co-production with the Public Theater of “The Intelligent Homosexual’s Guide to Capitalism and Socialism With a Key to the Scriptures” (also directed by Greif) and “The Illusion.”

The two parts of “Angels” — “Millenium Approaches” and “Perestroika” — will play in alternating rep for the entirety of the Signature run. Official opening night is set for Oct. 28.