Melbourne (AFP) - Mixed martial arts star Ronda Rousey and challenger Holly Holm scuffled and had to be separated at the official weigh-in on Saturday ahead of their weekend title fight in Melbourne.

As the American UFC bantamweight champion approached Holm for the obligatory stare down, the challenger put her fist in Rousey's face and she responded with a raised elbow to swat her away.

Then a war words erupted as a fired-up Rousey started a shouting match with the former boxing world champion, who loudly declared: "I am here to shock the world."

Rousey put all the blame for the incident on Holm while calling the New Mexico native "fake".

"I just wanted to get in her face and show her that I was there for a reason," Rousey told reporters.

"She put her fist on my face. I didn't touch her, she touched me.

"I told her that fake, sweet act... I can see right through it.

"All that respect, all you being sweet I see right now it is fake and you're gonna get it on Sunday.

"It's not the first time your camp thought they had the perfect plan to beat me.

"I'm going to show you on Sunday why I'm the champ."

Rousey boasts a 12-0 record and organisers are hoping for a sell-out 63,000 crowd at Melbourne's Etihad Stadium.

Rousey, a former Olympic judoka, has helped push mixed martial arts into the mainstream of US sport with a series of dynamic knockout victories that have earned her comparisons to Mike Tyson's rise in heavyweight boxing during the 1980s.

Holm is also undefeated in the sport with a 9-0 record.

The pair had initially been due to fight in Las Vegas on Jan 2 but the contest was brought forward in a bid to spread Rousey's appeal to another corner of the globe.