A Brazilian passenger jet was forced to make an emergency landing on Saturday after a man went on a rampage, got into the cockpit and assaulted the pilot.

The TAM Airlines plane had been flying from Montevideo, Uruguay to Sao Paulo when a man entered the cockpit when the door was open, AP reports.

Witnesses have said the plane then dove to the right and the pilot yelled for help.

One passenger told El Pais newspaper in Uruguay "two stewardesses came out asking for help and grabbing a young man by his feet".

"The people quickly jumped on top of him, the guy fought back furiously, biting and hurting a half dozen people."

Another passenger, Matias Velazco, told El Observador it took 10 minutes for passengers and crew to subdue the man.

"One tried to give him an injection to sedate him, another hit him and still they couldn't control him," he said.

Uruguay's Industry Minister Roberto Kreimerman was on the flight and told the newspaper passengers screamed and feared for their lives when the plane veered sharply.

The plane landed safely at an airport in southern Brazil about 20 minutes later. A police spokesman said the suspect was arrested and taken to a facility for mental care.

The airline has confirmed an emergency landing was made "because of an uproar on board" but did not elaborate.

Some passengers have claimed the man was wearing a TAM identification badge.