Britain's vote to leave the European Union raises "longer-term concerns" about global growth at a time of already weak economic output, US President Barack Obama said Wednesday.

"I think there are some genuine longer-term concerns about global growth if, in fact, Brexit goes through and that freezes the possibilities of investment in Great Britain or in Europe as a whole," Obama said, speaking at a North American leaders summit. 

"At a time when global growth rates were weak already, this doesn't help."