New Zealand captain Kane Williamson hailed the T20 World Cup's expansion to 20 nations after co-hosts United States beat Pakistan on Thursday in one of the biggest upsets in the tournament's history.

The World Cup, also co-hosted by the West Indies, has an extra four teams, giving fledgling cricket nations more big-tournament experience while also raising concerns their presence could mean more one-sided results.

Williamson, who made his T20 World Cup debut in 2012 when Sri Lanka hosted 12 teams, said the bigger field was a "fantastic thing".

"That sort of exposure is only beneficial for all teams," he told reporters on a video call from Guyana.

"When you come to tournament-time anything can happen which is the beauty of the sport.

"But it's ultimately great for the growth (of cricket)."

The USA, who were guaranteed entry as co-hosts, pulled off a Super Over win against Pakistan in Dallas after beating fellow tournament debutants Canada.

The undefeated Americans are now top of Group A before playing heavyweights India next week. The top two in the group advance to the Super 8 phase.

Williamson said his team had watched the Pakistan upset from their base in the Caribbean.

"That was an amazing game of cricket," he added.

"In these tournaments every team has really talented players, whether they've had experience against test-playing nations or not.

"In some ways, it's (how you play) on the day."

New Zealand, bidding for their maiden World Cup title, kick off against Afghanistan in Guyana on Friday, having waited long to get into the action.

"We're one of the last teams to start so I know we're all looking forward to starting off the tournament after spending maybe 10 days or so practising," he said.