MONTAUBAN (AFP) - Mark Cavendish took another giant step towards Tour de France greatness by claiming his 29th stage win on Thursday in a dramatic sprint finish in sweltering heat.

The 31-year-old Briton now only has Belgian legend Eddy Merckx ahead of him on the all-time list of stage victories with a once-seemingly unattainable mark of 34.

But having won three stages out of six already in this Tour, Cavendish is coming up fast behind Merckx, a five-time Tour winner.

On Thursday's 190.5km sixth stage from Arpajon-sur-Cere to Montauban, Cavendish timed his burst for the line to perfection to streak past Marcel Kittel and then hold off a late surge by the German.

Briton Dan McLay took a surprise third place on the stage to show the future is bright in British sprinting whenever former world champion Cavendish decides to call time on his remarkable career.

The Manx Missile had already beaten Kittel into second on Saturday's opening stage to Utah Beach before also winning the third stage in Angers.

Kittel got his own back on Tuesday's fourth stage when Cavendish could finish only eighth but the Briton proved in Montauban he's the fast man to beat at this Tour.

He also took back the sprinters' green points jersey from Slovakia's Peter Sagan.

It's a jersey he should keep for several days as the Tour passes through the Pyrenees, where the overall contenders will finally start their battle.

Belgium's Greg Van Avermaet kept hold of the race leader's yellow jersey and maintains his 5min 11sec lead over Frenchman Julian Alaphilippe.

But both will be hard pushed to maintain such lofty positions on Friday when the first major mountain, the Col d'Aspin, looms large.

Spain's Alejandro Valverde, third at 5:13, is well placed to take over the race lead but his Movistar team leader Nairo Quintana and reigning champion Chris Froome will also be aiming to make their mark.

They are only another four seconds back.

On a scorching hot day, there was a certain inevitability of a bunch sprint at the finish.

With searing heat accompanying the riders all day, only two men found the courage to embark out on a lonely, long-range bid for glory.

Japan's Yukiya Arashiro was joined by Czech Jan Barta on a day that began with a summery 25 deg C temperature in Arpajon but ended in a sweaty 32 deg C in Montauban.

During the first half of the race they built up a lead of 5min 15sec but the conditions took their toll and the gap dipped down to under a minute with more than 40km still to ride.

The end for the duo came 22km from the finish as the sprinters' teams took no chances.

Kittel seemed well set in the sprint but Cavendish had his wheel and stormed past to take another memorable win.