MARTIN Guptill could not have found a better time to rediscover his form as he scored a World Cup best 237 not out to lead New Zealand into the semi-finals against South Africa.

Guptill's innings, which eclipsed Chris Gayle's 215 from earlier in the tournament, anchored New Zealand's 393 for six that gave the World Cup co-hosts a 143-run victory in their quarter-final against West Indies.

The score was the first one-day international double century by a New Zealand batsman and followed the 105 he scored against Bangladesh in the final pool game on March 13.

"I'm still not really sure what happened today," Guptill said. "It hasn't sunk in yet. I am incredibly proud of today and hopefully moving forward we can win another game and then another one after that."

A firing Guptill has shortened the odds of Brendon McCullum's side becoming the first from New Zealand to lift the World Cup, though until last week the 28-year-old seemed to be struggling to build an innings.

He made 49 in the opening game against Sri Lanka and then only managed 17, 22 and 11 in the next three matches before he scored 57 against Afghanistan. That released the pressure valve and Guptill began to do what he does best against Bangladesh: play straight, work the ball into gaps to turn the strike over and, when it was full, loft the ball in the arc between wide mid-off and deep mid-wicket. He repeated the recipe yesterday against the West Indies.

Guptill, who lost three toes in an industrial accident as a teenager, was roared off the field by the 30,268 crowd in Wellington and he admitted that he had never felt he would experience that feeling.

"It's pretty cool. I've never heard anything like that before," he said.

McCullum said it was one of the best innings seen in one-day cricket.

"Sublime, just sublime," the New Zealand captain said. "I will never forget it. The innings we witnessed is probably one of the best we have seen in this format.

"We wanted to make a real statement on the back of Gup's innings and that's what we did with the ball and in the field. We will celebrate Gup's success, the team's success and then turn our attention to the semi-final."

West Indies captain Jason Holder said Guptill, who was dropped on four from the third ball of the match, had played brilliantly.

"A set batman on that pitch is dangerous. Having said that we didn't bowl our yorkers well," he added.

New Zealand pace bowler Trent Boult, who took four wickets to overhaul Australia's Mitchell Starc as the tournament's top wicket taker, said he rated Guptill's innings as the best he had seen.

"It was nice to go out and bowl well as a unit in a pretty difficult situation, they were coming out there to give it everything. It's on to Auckland now and hopefully we can make it some more good memories," he said.