A crowd lined up three-deep cheered on Harry Ko as he put on the performance of a lifetime.

But this was no sporting challenge or game. Mr Ko was one of the home-town favourites who made it to the semi-finals of the unofficial coffee Olympics.

Dozens of the world's best coffee makers and brewers have converged on Melbourne for the World Baristas Championship and World Brewers Cup, the biggest competitions in the world of coffee.

Entrants must win national competitions to qualify, often with the help of a coach and extended support team that could include food scientists.

This is the first time the event has been held in Australia, and Mr Ko spent more than six years trying to make it to the competition.

"I love pressure with so many people watching me," Mr Ko told AAP, moments after stepping off stage.

The reigning Australian brewing champion was running on adrenalin as passers-by stopped to congratulate him on the three beverages he had served up to the judges.

"If I reach the final in this round, oh my god that would be really, really fantastic," Mr Ko said.

The top three in the competition win far more than just gold, silver and bronze trophies in the shape of coffee pots.

Finalists find doors across the global industry quickly open to them, with many winners going on to open their own businesses. One was even featured in a film.

At the other end of the Melbourne Convention and Exhibition Centre, Italian barista champion Matteo Pavoni has just completed his 15-minute routine.

He served up three kinds of coffees using a specially designed roast created with the help of a chemist at the University of Oregon.

The taste of the coffee is just one part of the challenge, with four judges marking him on everything from his explanation about how the drinks were formulated, to how he used particular methods.

"It's incredibly competitive," Mr Pavoni tells AAP.

"I've never seen such a high level of coffee preparation before."

The first-time competitor hopes he will make it into the final round on Friday, but is just grateful to be considered one of the top 16 baristas in the world.

The competitions are being held at the Melbourne International Coffee Expo, an exhibition expected to attract more than 10,000 industry heavyweights and coffee fanatics from all over the world.

Grandstands capable of seating hundreds of people were set up in preparation for Friday's finals, with organisers expecting them to fill up very quickly.