The Cannes Film Festival has come under scrutiny for its policy of only allowing women dressed in high heels to walk on the red carpet for its formal premieres.

Many are criticising the festival after Screen International reported that several middle-aged women were turned away from the Sunday premiere of Carol for wearing flats.

Actress Emily Blunt called the report "very disappointing".

Sicario director Denis Villeneuve joked that he, Benicio del Toro and Josh Brolin would wear heels to the evening premiere in protest.

The red carpet at Cannes is highly regulated by tradition. Men are expected to wear tuxedos, women dresses and heels. The dress code is not explicitly spelled out by the festival but is enforced by security guards.

"Everyone should wear flats, to be honest, at the best of times," said Blunt, who was there to premiere the Mexican drug war thriller Sicario. "You kind of think that there's these new waves of equality."

Festival spokeswoman Christine Aime suggested that festival staff (hosts) had made a mistake.

"There is no specific mention about the height of the women's heels, as well as for men's," Ms Aime said of Cannes's dress code. "Thus, in order to make sure that this rule is respected, the festival's hosts and hostesses were reminded of it."

Some were already calling the incident Shoegate.

Asif Kapadia, the director of the Amy Winehouse documentary Amy, added on Twitter that his wife was also initially refused entry to his film's Cannes premiere on Saturday because she was not wearing heels, but she was eventually allowed in.

The dust-up is particularly awkward for Cannes because this year's festival has been marked by considerable discussion about gender equality in the film industry.