Florian Wirtz scored a hat-trick as Xabi Alonso's Leverkusen sealed their landmark triumph in style, continuing their unbeaten campaign to beat Werder Bremen 5-0 on Sunday.

It's the club's first-ever German league title with five games remaining as they lead second-place Bayern Munich by 16 points with just five matches left, an amazing achievement carved out by their soaring Spanish coach Xabi Alonso.

Fans had already stormed onto the field when Leverkusen scored their fourth goal with seven minutes to go, and the final minutes were played in thick red smoke from supporters' pyrotechnics as players on their bench clapped along to songs, danced and hugged one another.

The fifth goal in the 90th brought more fans onto the field -- hundreds this time -- and the referee ended the game amid confusion and jubilation.

Thousands of supporters crowded the field waving flags, flares and cardboard copies of the Bundesliga trophy.

Leverkusen finally shed their reputation as perennial runners-up after five second-place finishes in the league and one in the Champions League.

And Alonso believes their triumph could be a breath of fresh air for German football after Bayern's monopoly.

"I am happy for everyone," he said.

"Perhaps it is healthy for the Bundesliga and German football for other teams to win. We have to enjoy it. It is a super moment. Now it is time to celebrate. Today we have deserved it."

Victor Boniface settled Leverkusen's nerves with the opening goal from the penalty spot before Granit Xhaka hit an audacious long-range shot to make it 2-0 with half an hour to go.

Bremen folded after that with substitute Wirtz scoring a goal very similar to Xhaka's, then another on the counter in the 83rd and a third to end the game, his first career hat-trick.

The public address system played "Viva Espana" as a tribute to their Spanish coach Alonso, who could be on for a trophy treble as well as un unbeaten season.

They visit West Ham in their Europa League quarter-final second leg on Thursday with a 2-0 lead, but will hope the fans have not done too much damage to the BayArena ahead of any semi-final.

Leverkusen also meet second division Kaiserslautern in the German Cup final on May 25.

"We can focus on West Ham soon but not tonight. Next week is something else. The players are a top, top team, they are top, top lads," said Alonso.

"For this season, we still have big goals. It is a very good spot for me to be. This feeling is unbelievable."

Alonso, who was soaked with beer amid a massive pitch invasion, has turned down the chance of taking over former clubs Liverpool and Bayern to stay at Leverkusen and he remarked: "It was the right decision."

With DPA

Australian Associated Press