The semi-finals of the event will be staged in St Lucia alongside the men's tournament on May 13 and 14.Australia secured its place in the last four after a 24-run victory over South Africa in the first game of the day on Friday at Warner Park with all-rounder Shelley Nitschke leading from the front.
The West Indies sealed its place in the semi-finals after defeating reigning champion England by just two runs. Charlotte Edwards' side, chasing 123 runs for victory, could finish at 120 for nine.
The wickets were shared between Shermaine Campbelle (2-15), Deandra Dottin (2-31) and Anisa Mohammed (2-9), the latter being named Player of the Match.
In the first match of the day, Australia made a fantastic start to its innings after being put into bat by South Africa captain Cri-Zelda Brits.
Alongside Nitschke, Leah Poulton made a quick-fire 39 off 25 balls and Jess Cameron struck 27 runs off 18 balls.South Africa's Sunette Loubser (3-22) and Shabnim Ismael (3-30) were the pick of the bowlers while Brits, Angelique Taai and Loubser showed quick reactions with each running out an Australia player during the innings.
South Africa's batting line-up flopped despite a valiant effort by number-three batter Mignon du Preez who finished on an unbeaten 53 that included four fours and two sixes.
Australia proved to be superior in the field, limiting South Africa to 131 in 20 overs and thus securing itself a spot in the semi-finals of the tournament and knocking South Africa out.
In the second match of the day, the West Indies defeated the current champions in front of a large and excitable crowd in the St Kitts afternoon sunshine.
The host, put into bat, scored 122-8 in 20 overs with Britney Cooper the only batter of any significance, making 20 off 14 balls. Dottin, who in the side's previous match scored a century, departed for a first-ball duck.
England's Laura Marsh took 3-17 and Jenny Gunn scalped 2 for 10.As England took to the field, Charlotte Edwards and Sarah Taylor wasted no time and clocked up 65 runs between them in nine overs before Edwards departed for 31 after being caught by Cordel Jack.Sarah Taylor departed not long after that and only Lydia Greenway managed to make any runs of note, finishing the game on 26 not out.Claire Taylor once again failed to put runs on the board, this time departing for four.