Max Verstappen capped a dominant season on Sunday when he clinched back-to-back Formula One world titles with victory at a wet Japanese Grand Prix.

Red Bull driver Verstappen got a 12th season win from 18 races ahead of teammate Sergio Perez and Ferrari driver Charles Leclerc, who originally crossed the line in second but was handed a five-second penalty for going straight in the final chicane under pressure from Perez.

That incident not only cost Leclerc second place but also handed the world title to Verstappen.

It was originally believed that full points would not be awarded because the race did not go over the full distance after being red-flagged and interrupted for some two hours, which would have meant that Verstappen would have missed out by one point.

Confusion reigned when Verstappen was suddenly declared champion – and it then became clear that full points were awarded after all because the suspended race was resumed and not abandoned.

Securing the title with four races to spare stood in sharp contrast to last year when he had beaten Mercedes driver Lewis Hamilton for the title in the last lap under controversial circumstances at the season-ender in Abu Dhabi.

Leclerc started strongly into the season but Verstappen was soon in full command with his reliable Red Bull while mistakes from Leclerc and Ferrari also worked in his favor.

"It's crazy," Verstappen said. "What a year we've had so far. It's been incredible.

"It's something I could never have imagined after last year, fighting until the end, and then having such a good car again this year. I'm so thankful to everyone who has been contributing to this success."

Sunday's race was red-flagged shortly after the original start due to rain and bad visibility, with pole sitter Verstappen just edging Leclerc to stay first.

But conditions quickly became unsafe as Ferrari's Carlos Sainz crashed out due to aquaplaning and Alex Albon of Williams also went out with a technical problem.

Action did not resume until more than two hours later, with a rolling start in slightly better conditions and full wet tires mandatory.

However, Sebastian Vettel of Aston Martin and Williams driver Nicolas Latifi soon switched to intermediates which proved a good move as both climbed up the field quickly – and everyone else soon pitted as well.

Verstappen pulled away from Leclerc and was untroubled in victory but at the time no one knew that the win – coupled with Leclerc's penalty – also meant that the title was his.

"We thought it wasn’t going to be full points awarded. We thought we were one point short," team principal Christian Horner said.

"That’s beyond all our dreams. Max has been truly dominant. We came back from some difficulties in the first couple of races, but he and the team have just raised it to another level."

Earlier, a recovery tractor had appeared on the track after Sainz's crash before the cars had returned to the pits under the red flag – sparking a safety debate.

In 2014, Jules Bianchi's car slid off the same track in similar conditions and hit a recovery vehicle, dying the following year of the injuries sustained.

"I still don’t know why we keep risking, in these conditions, having a tractor on track. You were going to red flag it anyway, so why risk it?" Sainz said.

Horner called for a full investigation as he said: "We lost Jules Bianchi here eight years ago, and that should never ever happen."

Perez tweeted: "How can we make it clear that we never want to see a crane on track? We lost Jules because of that mistake. What happened today is totally unacceptable!!!!!"

"I hope this is the last time ever I see a crane on track!"