Red Bull's Sebastian Vettel roared into the record books as Formula One's youngest double world champion on Sunday after finishing third in a Japanese Grand Prix won by McLaren rival Jenson Button.

- Japan GP: Podium finish for Vettel, wins his second F1 title

The boyish 24-year-old German, who had started from pole position for the 12th time this season, had needed only a point at Suzuka to clinch his second successive crown with four races to spare.

Ferrari's Fernando Alonso, the previous youngest double world champion when he won for Renault aged 25 in 2006, was a close second to Button on a beautiful sunlit afternoon at the Honda-owned circuit.

"Thank you so much, every single one," said Vettel, his voice trembling with emotion as he choked back the tears behind his visor, over the team radio after being told he was the 2011 world champion.

"We took nothing for granted and we did it."

There was to be no trademark raised digit as race winner but he was number one again anyway, only the ninth driver to take back-to-back championships and on the podium for the 14th time in 15 races this year.

Vettel, congratulated by both Button and Alonso afterwards, now has 324 points to Button's 210 and Alonso's 202.

He had vowed to retain the title in style and his aggression and determination was evident from the start as he cut across Button and forced the Briton onto the grass.

"He's got to get a penalty for that," Button shouted over the radio but stewards, who included Australia's 1980 champion Alan Jones, decided to take no further action after reviewing the incident.

The German pulled away initially at a second a lap but 2009 champion Button reined him in and took the lead at his second pitstop when he emerged just ahead of the German in a race dictated by tyre wear.

"I think we were a little bit too weak today on the option tyre," said Vettel, who has been otherwise dominant in his charge to the title after seizing his first against the odds in the final race last year.

"To win the championship here is fantastic. So many things you want to say in this moment but it's hard to remember all of them," he added. "There are so many people, it's hard to name them all to thank them."

A safety car incident triggered by another coming together between McLaren's Lewis Hamilton and Ferrari's Felipe Massa, as well as a contact between Red Bull's Mark Webber and Mercedes' Michael Schumacher, bunched up the field for three laps while marshals retrieved debris.

Button kept his lead and took the chequered flag for what he considers a second home race, thanks to his Japanese girlfriend and long-standing passion for the country, just 1.1 seconds over Alonso.

"It was a great race, the start was very good -- maybe too good and I ended up on the grass," grinned Button, ecstatic at his third win of the season and 12th of his career.

"It's always a very special place to race, Suzuka. This is one of the most perfect places to race and the crowd are very special. It's one of our most special victories, it means a lot to me," added the Briton, who had written off his own title chances long ago.

Just as he had when he won in Monaco in 2009, his title year, Button parked his car in the wrong place and ran back up the pit lane waving to fans.

Alonso had threatened to take the win but Button had just enough in his tyres to keep him at bay. Vettel was only 0.8 seconds further back.

The win cut Vettel's overall lead over the Briton to 114 points, an insurmountable advantage with a total of 100 left to be won.

Hamilton, who has had numerous calls to the authorities this season, finished fifth after stewards took no further action for the incident with Massa that ripped off the Ferrari's front wing endplate.

Australian Mark Webber, still without a win this year, was fourth for Red Bull, who have 518 points to McLaren's 388 and could wrap up the constructors' championship in South Korea next weekend.

Schumacher, who briefly led the race during the pitstops, was sixth and Massa seventh.

In a race of only one retirement, Mexican Sergio Perez was seventh for Sauber ahead of Renault's Russian Vitaly Petrov.

Germany's Nico Rosberg, who started on the back row after failing to set a lap in qualifying, roared back to take the final point.