Lewis Hamilton has admitted he is "under no illusion" of being favourite to clinch the driver's title this season, despite holding a relatively comfortable lead over his main challenger Sebastian Vettel.

The Briton enters this weekend's Japanese Grand Prix in Suzuka 34 points ahead of the Ferrari driver, who has suffered a catalogue of issues over the last two races in Singapore and Malaysia.

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Ferrari have outpaced Mercedes in both races, but Vettel and teammate Kimi Raikkonen crashed into each at the first corner in Singapore, while the German could only finish fourth last week after starting from the back of the pack due to an engine problem.

Raikkonen, meanwhile, failed to start the race, despite qualifying second.

Hamilton won in Singapore and finished second in Malaysia, meaning he has gained 31 points over his rival in the last two events and is favourite to secure his fourth world title. However, with 125 points still up for grabs in the remaining five races, the 32-year-old is taking nothing for granted.

"I am under no illusion," he was quoted as saying by the BBC.

"I might have the nail a little bit in, but I need to keep hammering it. It is not done until there is no more to push it in."

Earlier this week, the Briton said Mercedes have "big problems" heading into the final two months of the season and admitted he was concerned by the progress made by Ferrari over the last two races, even if it did not bear tangible results for the Scuderia.

Having won his maiden title on the last turn of the final race of the season in 2009, Hamilton is well aware of the capricious nature and unpredictability of the end weeks of the campaign.

"There are so many points available and you have seen other years where things swing," he added.

"The pendulum can swing. I am hoping if it starts to swing the other way we have enough force to push it back to where it should be.

"Each race is really just about trying to understand more about the car because there is constantly something new coming in the mix that can catch us off guard."

Meanwhile, Ferrari have confirmed that Vettel's gearbox is not damaged following his crash with Lance Stroll after the chequered flag fell at last weekend's Malaysian Grand Prix.

That means the German will avoid a five-place grid penalty, which would have automatically kicked in if he needed a new unit as the rule stipulates that one single gearbox has to last through six races and Vettel's was changed just before the contest in Sepang.

"We have a chance," the four-time world champion said when asked of his prospects of catching Hamilton at the top of the standings.

"I tend not to rate many things. I think there is a chance and we make sure we use it.

"We are behind so it depends on what Mercedes are doing. We just have to do our best and we need to score much more than them. How we achieve it doesn't matter as long as we do achieve it."