All hail Macbeth, that shalt be king hereafter.
The earth hath bubbles, as the water has, And these are of them. Whither are they vanish'd?
Which of you have done this?
As the witches meet with Macbeth, they tell him his prophecies and how he will become king. The witches praise him by saying, "All hail Macbeth, that shalt be king hereafter" (1.3.48) to lure him into their tricks of trust. Having the witches correctly determine Macbeth's life outcomes further shows their supernatural capabilities.
When Macbeth is with Banquo while visiting the witches, after their encounter, the witches suddenly vanish. After the witches disappear, Banquo says "The earth hath bubbles, as the water has, And these are of them. Whither are they vanish'd?" (1.3.77-78). This shows his genuine concern for the witches' whereabouts. When the witches vanish, it is none other than a supernatural occurrence. 
In Act 3, when Macbeth hosts a dinner party, he goes to take his seat but it is taken by none other than Banquo's ghost.  Macbeth panics, asking people around him who has done this, but to his surprise, only he sees the ghost. When Macbeth says, "Which of you have done this?" (3.4.48) we can see how at first it did not register that he is seeing something supernatural. This represents an example of a supernatural appearance.