Martin Guptill smashed an unbeaten 237 from 163 balls against West Indies.
The 28-year-old opener's total surpassed the previous World Cup best of 215 made by Chris Gayle.
Currently, West Indies are five for the loss of a wicket after three overs, with opener, Chris Gayle on 11.
Martin Guptill's innings was also the highest individual score in World Cup history.
Trent Boult is now the joint second highest wicket-taker with 17 scalps and joins India's Mohammed Shami on third.
Guptill's innings also saw him break his own record for the highest ODI score by a New Zealander.
He also became the second man after Chris Gayle to do so at the grandest stage.
Martin Guptill was dropped on four by Marlon Samuels — a chance that cost West Indies dearly.
Currently, New Zealand are 374 for the loss of six wickets after 49 overs, with opener, Martin Guptill on 217.
Currently, New Zealand are 343 for the loss of five wickets after 47.1 overs, with opener, Martin Guptill on 203.