Why does Hamlet's departure have special urgency?

Basically they are looking for Polonius's corps. Immediately after Hamlet exits, dragging Polonius’ body, we see Claudius asking Gertrude to explain what has happened. She tells him of Hamlet’s accidental killing of Polonius and Claudius realizes that he could have just as easily been slain. Claudius asks where Hamlet has gone and Gertrude says that he has taken the body away. The king orders Rosencrantz and Guildenstern to find Hamlet and discover where he has taken Polonius’ corpse. The King has to find Hamlet before he does any more damage.