Gennady Golovkin says Canelo Alvarez is his biggest challenge yet and capable of ending his unbeaten streak. (1:10)

Saul 'Canelo' Alvarez expects a knockout when he challenges world middleweight No. 1 Gennady Golovkin on September 16.

The Mexican meets Golovkin for his WBC, IBF and WBA belts at the T-Mobile Arena in Las Vegas in one of the most significant fights in recent boxing history and the biggest since the welterweight title fight between Floyd Mayweather Jr and Manny Pacquiao in 2014.

Alvarez (49-1-1, 34 KOs), 26, does not believe the fight will disappoint after coming face-to-face with knockout specialist Golovkin (37-0, 33 KOs) at a press conference in London, the first leg of a global media tour to promote their fight.

"I have to be careful with everything when facing him because he's good all around," Alvarez told a press conference Monday.

Alvarez meets Golovkin for his WBC, IBF and WBA belts at the T-Mobile Arena. Getty Images

"There's a lot of probability there will be knockout, as we can both punch. I'm Mexican and he's trained by a Mexican [Abel Sanchez] and the fans are in for a treat. There's a high probability there will be a knockout.

"I'm going to have to be smart and elusive to avoid his punches. He's very powerful if you stand in front of him."

Glolovkin, 35, has made 18 consecutive world middleweight title defences but was given his toughest test yet in his last outing against American Daniel Jacobs in March, which was the first time he had been taken to points since 2008.

But Kazakhstan's California-based Golovkin admits Alvarez will be his toughest test yet.

"This is the most difficult," said Golovkin.

"Canelo is ready, 100 per cent. I know him, he's the best. I have a plan, my coach Abel Sanchez has a new idea.

"His power, his timing, he has a good team, he lives well, he has everything. He's tough."

Billy Joe Saunders, the WBO world middleweight champion from the UK, was also at the press conference sat among the media and asked Alvarez why he had relinquished the WBC title and not fought Golovkin sooner.

"There were a lot of conditions from the WBC and a timeline, they put conditions in the purse split," said Alvarez through a translator.

"I had a court case in Miami and they wanted to negotiate with them [Golovkin's management team] within 15 days. I couldn't do it."

Saunders wants to fight the winner, but Golovkin is unimpressed after talks to face the Briton have previously stalled.

"You talk too much, you are a boxer, not a promoter," said Golovkin to Saunders.

Golovkin-Canelo will follow Floyd Mayweather Jr's comeback against Conor McGregor at the same Las Vegas venue on Aug 26.

American Mayweather is returning from two years retired to face Irishman McGregor and could make more than the record $623.5 million which Mayweather's win over Pacquiao brought in three years ago.

Mayweather-McGregor has been called a "ridiculous" mismatch by the likes of former world heavyweight champion Lennox Lewis, and Oscar De La Hoya, Alvarez's promoter, made a veiled dig at the event that threatens to overshadow Golovkin-Alvarez.

"Both fighters have the type of action packed style that the fans clamour and something fans will not see in any other fight this summer," said De La Hoya.

"You have two fighters here who are stepping up and fighting the very best. I know for a fact that what you have seen from Gennady has been amazing and what you have seen from Canelo has been incredible. But they are going to step up their game and move on to a new level."