ATCT GND CTLR LOOKED UP IN TIME TO SEE A CESSNA TKOF RWY 25R AS AN SMT WAS TAKING OFF ON RWY 30. RPTR SHOUTED AT THE LCL CTLR; BUT THERE WAS INSUFFICIENT TIME TO TAKE ANY ACTION. THE CESSNA HAD BEEN CLRED TO LAND AND MADE A TOUCH AND GO INSTEAD AND HAD AN NMAC AT THE INTXN OF THE RWYS. PLT DEV.

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SIMULTANEOUS RWY OPS WERE IN EFFECT FOR INTERSECTING RWYS 30 AND 25R. I WAS WORKING GND CTL. SOMETHING URGENT CAUGHT MY EYE AS OBSERVED TWO DEPARTING ACFT CONVERGING DIRECTLY TOWARDS EACH OTHER AT THE INTXN. ONE WAS LIFTING OFF RWY 25R; A CESSNA; AND THE OTHER WAS LIFTING OFF RWY 30; A TWIN BEECH. I SHOUTED AT THE LCL CTLR TO 'LOOK OUT' AS I POINTED TO THE INTXN. THE CTLR WAS WORKING BOTH DEPS. TFC WAS IMMEDIATELY ISSUED BUT THE CESSNA CROSSED IN FRONT AND BELOW THE TWIN BEECH JUST BARELY. THIS WAS SECONDS AWAY FROM A MIDAIR COLLISION. I FEEL THE PLT OF THE CESSNA SHOWED A LACK OF AWARENESS. APPARENTLY HE WAS A STUDENT PLT. I WILL ONLY ADDRESS THIS SIT; BUT TOO MANY TIMES I SEE STUDENT PLT FLYING INTO SITS WHERE THEY HAVE NO IDEA WHAT'S GOING ON AROUND THEM. IN THIS SIT; THE PLT WAS CLRED TO LAND AND RESTR TO 'HOLD SHORT OF RWY 30 FOR DEPARTING TFC.' HE ACKNOWLEDGED WITH HIS CALL SIGN. WHAT HE DID WAS A TOUCH AND GO. SOLUTIONS: DON'T ALLOW THESE PLTS TO FLY BY THEMSELVES TOO EARLY. FROM THE ATC SIDE; PERHAPS MORE CTLRS WOULD HAVE PREVENTED THE SIT. THE CTLR'S COORDINATOR POS WAS NOT OPEN. THAT POS COULD HAVE ENSURED THE PLT READ BACK HIS HOLD RESTR WHICH HE DID NOT DO.