Organisers of the Melbourne International Film Festival have been forced to shut down online ticket sales after Chinese hackers booked out all film sessions on its website.

The attack comes as part of a mounting campaign against the screening of a documentary about exiled Uighur leader Rebiya Kadeer.

Hackers broke into the festival's website soon after the launch of the 2009 program, replacing festival information with the Chinese flag and anti-Kadeer slogans.

Six Chinese language movies have also been pulled out of the festival, leaving organisers with a logistical headache and the fear that Chinese filmmakers will boycott the festival in future.

The festival's website reads: "Online sales are currently offline due to a denial of service attack of Chinese origin."

Spokeswoman Asha Holmes said all sessions on the site had posted "sold-out" messages about 9am AEST today.

She said it was not immediately known whether the rush on tickets was real. But when the bookings were traced to Chinese websites, it soon became clear they were fake.

"It's under attack again," Ms Holmes said.

"People have been unable to book sessions at all."

Internet technicians have been unable to keep up with the speed of "shopping carts" filling once the sessions have been cleared of the fake bookings, she said.

Film buffs can still buy tickets at the festival's box office or over the phone.

- AAP