This is a clip from 'Troop of One Hundred', taken from a Japanese comedy/prank show, where a 100 people chase after random strangers and you see their reactions. Totally harmless but their reactions are priceless.
For a translation of what they're shouting (thanks Digg):
- For the 1st and 2nd guys, they shout: "There's a tsunami!!" (tsunami da!)
- For the 3rd guy they shout: "That's the guy!!" (koitsu da!)
- Nothing for the 4th guy
- Last scene: "Watch out!! (danger)" (abunai!)