Hamilton has won four out of the first six races this season

Lewis Hamilton says he is determined to race in Formula 1 for as long as possible so he does not "squander" his opportunity to keep winning.

The Mercedes driver has won four of the first six races this year and is 14 victories short of Michael Schumacher's record of 91 grand prix wins.

"Michael retired when he was 38. I'm 33," said the five-time world champion.

"I can definitely do five years. I've got to keep going for as long as I can basically - until I'm not enjoying it."

Hamilton, who is actually 34 and was speaking on My Next Guest Needs No Introduction With David Letterman on Netflix, has won four of the past five World Championships.

He is leading in 2019 by 17 points from team-mate Valtteri Bottas, and said his desire for success is as strong as ever.

"I am ridiculously determined to win," said the Briton. "What really drives me, and I feel that the people I race against may lack somewhat, is that fire.

"I've got this opportunity. I could easily let go of it right now but I feel like I would be squandering it if I didn't continue to improve, grow and push."

Hamilton also said he had battled "mental issues" as a result of the demands of F1.

"It's a hard, hard year," he said. "Mentally you have these massive highs, wins and success, but then you have these massive comedowns.

"[It's] something I've never really spoken about but you often do suffer from mental issues - instabilities - and keeping yourself together when you hit rock bottom, which you do as an athlete.

"If you're lucky you can find strength at rock bottom. It's about how you get up, not how you fall."

Can Mercedes keep winning in Canada?

Ferrari's Sebastian Vettel won in Canada in 2018, with Hamilton finishing the race in fifth place

Hamilton's next challenge is this weekend's Canadian Grand Prix, which he has won six of the past 11 times it has been held.

A victory at Montreal's Circuit Gilles Villeneuve on Sunday would put him level with German great Schumacher as the driver with the most wins on the historic track on the Ile Notre Dame.

However, Mercedes, who have won every race this year, may face a renewed challenge from Ferrari, whose car is expected to suit the track more than it did in the past two races in Monaco and Spain.

Mercedes F1 boss Toto Wolff said: "We are beginning to see more clearly the strengths and weaknesses of our car.

"In the past six races, we were very strong in the corners but lost time on the straights. This will make Canada a huge challenge for us as the track characteristics could favour our opponents - there are many long straights, and fewer corners in which to make up lap time. But we're looking forward to the challenge."

However, Mercedes are planning to introduce an upgraded engine for the Canadian race, which is likely to boost their pace assuming its use is approved ahead of the weekend.

Ferrari have let two opportunities to win this year slip through their fingers, in Bahrain and Azerbaijan.

Charles Leclerc suffered an engine problem in the closing stages in Bahrain after dominating the race and, in Baku, the Monegasque crashed in qualifying when looking favourite to take pole position.

Ferrari team principal Mattia Binotto said: "I think we will be in better shape [in Canada] compared to Barcelona, but the best car is still the Mercedes and should be ahead. But maybe the gap will close.

"We know we're not competitive enough right now and, for the time being, we haven't got any more changes coming on the car that will have a significant effect on the problems we have encountered since the start of the season.

"However, the Canadian track characteristics present another different challenge, given that top speed, braking efficiency and traction are the main considerations. We arrive here ready to do our best and to put the mistakes of the last few races behind us."