What are the locations of the Warp Zones in Super Mario Bros. 2?

In which levels are the Warp Zones located in Super Mario Bros. 2 (not The Lost Levels) and how do you get to them?

Solution 1:

Warp to World 4 - Go to world 1-3 and find a potion. Now find the vase next to the brick building all the way to the right side of the level. Drop the potion and go into Sub-Space and then warp into the vase (stand on top of it and press down) You will warp to World 4!

Warp to World 5 - Go to world 3-1 and go through the door to the large waterfall with all the clouds. Now jump down and land on the platform in the center and enter. Take the potion and drop it near the vase. Enter Sub-space and warp through the vase (press down on the vase) You will warp to World 5!

Warp to World 6 - Go to world 4-2 and get the potion. Now find the vase and put the sub-space door next to it (drop it from atop the vase) Now enter sub-space and warp. You now warped to World 6

Warp to World 7 - Go to world 5-3 and get the potion (make sure you can squat-jump to the vase, you need to get someone with a good jumping ability or use an enemy to give you a boost.). Put the sub space door near the vase and enter sub space and warp into the vase. You are now in world 7!

http://www.gamefaqs.com/nes/525244-super-mario-bros-2/cheats