The two teams meet in Cardiff today in the opening game of the tournament and Powell said that the Kiwis have improved greatly over the last year.
"They have done a lot of work in the last 12 months," said Powell. "We played them in the World Cup as England and they were a tough proposition and they are vastly improved.
"They worked really well throughout the game we faced them in, they brought a lot of pressure and they will run and run and run for 90 minutes.
"In all areas they are really striving to improve their game and they are getting better technically, so the game is a big challenge and we are expecting a tough encounter as they are quite strong in all areas."
Cameroon and Brazil make up the rest of the group.