Bayer Leverkusen coach Xabi Alonso said his unbeaten side was "not done yet" after winning their debut league title on Sunday with a treble still possible this season. 

Leverkusen's 5-0 win over Werder Bremen at home on Sunday, including a second-half hat-trick from Florian Wirtz, sealed a first Bundesliga title in their 120-year history.

Alonso -- who is in his first full season as a coach having joined Leverkusen midway through last season -- told reporters after the game the sky was the limit for his side, who are yet to lose a match in 43 games this season.

Soaking wet with beer after his players surprised him during the press conference, the 42-year-old manager reminded everyone "it's not over yet".

"We'll see how far we can go. I have a good feeling about it."

The win sent Leverkusen 16 points clear of Bayern with five games to go, meaning they cannot be caught. 

Their points total of 79 is the best after 29 games in German football history.

Leverkusen are through to the final of the German Cup and have a 2-0 lead after the first leg of their Europa League quarter-final with West Ham, with the second leg to take place on Thursday. 

"It's not over yet and we've got great goals we still want to achieve. But we can think about that on Tuesday. 

"Today and tomorrow, we need to celebrate."

Alonso pledged to stay at Leverkusen another year in late March, despite reported interest from Liverpool and Bayern Munich. 

Alonso, who retired after a glittering playing career with Liverpool, Bayern and Real Madrid, said his experience was an advantage working with players.

"I want to be near the players, talk to them and as someone who played I know what they're feeling.

"I have empathy and connection with the players, which is important in the dressing room. I try and keep this connection to the team."

Leverkusen have finished second five times but had never broken through for a German title. 

Alonso said: "This trophy belongs to a lot of people and we have to enjoy it."

Leverkusen's win broke an 11-year run of Bayern dominance. 

"It's perhaps healthy for the Bundesliga and German football that other teams win -- and it's a great pleasure that it's us," said Alonso.

One of the best decisions I've made

Another victim of a beer shower, which is tradition in German football, Leverkusen midfielder Granit Xhaka told reporters coming to the club "was one of the best decisions I've made in my life".

Xhaka moved to Leverkusen from Arsenal in summer, having spent seven years at the Gunners. 

Last season, Arsenal led the Premier League for much of the campaign, only to be caught by a treble-bound Manchester City. 

The Switzerland captain said: "When you start to first kick the ball as a child you think about titles.

"After seven years at Arsenal we nearly won the title last year. 

"I'm very thankful to be here and I was waiting so long for this moment."

Wirtz's second-half hat-trick sealed the victory and the 20-year-old midfielder said "at the start of the season we couldn't have imagined this".

"It (the belief) came gradually when we started winning a lot of matches with a dominant style of play. We said to ourselves we could do better than just have a good season and qualify for the Champions League."

Leverkusen winger Jonas Hofmann, 31, who won the Bundesliga for the first time after more than a decade in German football was emotional.

"I don't know whether to laugh or cry. We always pushed ourselves to the limit, that was just awesome."