Treble winners Bayern Munich crushed Schalke 04 8-0 with a hat-trick from Serge Gnabry and a superb debut from Leroy Sane on Friday as they made a sensational start to the new Bundesliga season and sent an ominous warning to potential challengers.

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Gnabry grabbed his first goal for the hosts with a fine turn and shot in the fourth minute in what turned out to be a one-sided affair that stretched Bayern's unbeaten run to 31 games this year, having now won the last 22 matches in a row.

Schalke, without a league win since January, were helpless against Bayern's lightning-quick game and Leon Goretzka found plenty of space to drive a low shot past keeper Ralf Faehrmann in the 19th minute.

Last season's top scorer Robert Lewandowski found the net with a 31st-minute penalty to become the first player to score in 10 successive appearances against the same Bundesliga opponents.

Gnabry then scored twice from Sane's assists in the 47th and 59th before Thomas Muller made it half a dozen.

Sane then capped a superb Bayern debut with a fine finish from a counterattack before substitute Jamal Musiala drilled in goal number eight to become the youngest ever Bayern scorer in the league at 17 years old.

Bayern finished their season in August when they added the Champions League to their Bundesliga and German Cup titles and then had only a short preparation for the new season.

"You can see that the team was already strong last season," said Sane, who joined from Manchester City. "The team is still hungry despite winning the treble last season and to have such a start is outstanding."

Bayern manager Hansi Flick lauded his side for the win.

"It was superb from us. Before the game we wanted this to be a game that would define where we are at this stage and my players did it very well," Flick said.

"We wanted to show that in this season again we are here."

Yet Flick was quick to point out that it was just one game in a long and crowded season to come.

"We just had the first game. Let us go slowly here. But it was important to show we are on the right path."

Schalke coach David Wagner, whose team has failed to win any of their last 17 league matches, rued his side's poor approach to start the campaign.

"Bayern were in sensationally good form," said Wagner. "At the moment Bayern are most likely the world's strongest team. They showed that today.

"We did not play well at all. We now need to shake it off and show a reaction [next week]."