A knife-wielding man wearing a balaclava tried to steal cigarettes and cash from a Nelson service station early this morning.
But the would-be robber was thwarted when a staff member activated a panic alarm.
Detective Sergeant Ian Langridge said the man entered the Mobil service station in Tahunanui about 3am armed with a small knife.
He demanded the staff member open the cigarette cabinet and till.
"The staff member has done the right thing by activating a panic alarm, and the man left without taking any property," Langridge said.