Vancouver Whitecaps starlet Alphonso Davies has joined Bayern Munich in a record-breaking $13 million deal, the highest transfer fee ever paid for a Major League Soccer player, it was confirmed on Wednesday.

Davies, who turns 18 in November, has signed a contract which runs from January 2019 until June 2023, the two clubs confirmed.

The Whitecaps said the deal could be worth up to $22 million if certain targets are met. US media reports said Bayern had paid a $13 million transfer fee for the winger.

"As a kid, I always dreamed of a moment like this," Davies said in a statement.

"Now that the dream has come true, the work continues as always. I have to keep pushing and keep striving, and also keep being me on the field. Ever since I joined the 'Caps when I was 14, they molded me throughout the years into the pro that I've become."

Davies will play the remainder of the MLS season before joining Bayern in January.

The transfer is the latest step on a remarkable rise for the teenaged Canadian international.

Davies was born in a refugee camp in Ghana in 2000 after his parents fled fighting in the second Liberian civil war.

When Davies was five his family moved to Canada as refugees.

His talent for football was quickly spotted and he joined the Whitecaps youth set-up in 2015 at the age of 14.

He made his MLS debut for Vancouver in 2016 and a year later played for Canada in the CONCACAF Gold Cup, finishing the tournament as joint top-scorer with three goals.

Vancouver co-owner Jeff Mallett meanwhile said the club was proud of Davies' progress.

"This is a landmark transfer for our club, country, and league," Mallett said.

"Youth development is a core part of our club. We provide player development opportunities across Canada through regional camps, tournaments, our national academy centres and Residency program.

"Alphonso is an inspirational example of what is possible, and we are excited about how this transfer showcases our commitment to homegrown players for our club and country."

Whitecaps president Ben Lenarduzzi added: "Alphonso is very special to us. We're happy to have him for the rest of this season and excited to see him take on this new challenge next year."