The film is well on track to surpass the record $21.6 million total gross of Moore's Bowling for Columbine - his 2002 film that earned him an Academy Award for best documentary.
Fahrenheit 9/11 has benefited from a flurry of praise and condemnation.
"It always helps when there's a group out there that says, 'Don't go see this movie. It's bad for you,'" said Jonathan Sehring, president of IFC Films, one of the film's distributors.
The documentary paints Bush as a neglectful president who ignored warnings before 11 September 2001, then stirred up fear of more attacks to win public support for the Iraq war.
The movie won the top honour at the Cannes Film Festival in May.
Beginning with the November 2000 US presidential elections, it opens with Democrat Al Gore apparently winning ... but then conceding victory to Republican Bush.
The camera pauses on Bush, who laughs nervously.
Then there is footage of Bush on vacation at his ranch in Crawford, Texas. Alluding to excessive amounts of holiday, the film pokes fun at the president.
"I'm working on some things," Bush awkwardly tells television news reporters, stumbling on his words three times.
"It always helps
when there's a group
out there that says, 'Don't go see this movie. It's bad for you'"
president of IFC Films
When the movie turns to the 11 September 2001 attacks in the US, the screen goes dark, leaving only the sound track- the explosions and the cries of anguish.
The film then moves to Iraq, where a woman is seen crying after her uncle's home is destroyed in a US bombing. "What have they done?'' she wails.
In another moving scene, the mother of a US soldier killed in Iraq breaks down in sobs as she talks about her son's death, doubting the reasons for going to war.