VISTA, Calif. -- A slim thief wearing a blue polka-dot shirt robbed a North County bank Thursday, and sheriff's deputies say the man claimed to be carrying a concealed gun.

The robbery at the US Bank branch at 640 Hacienda Drive in Vista was reported shortly after 2 p.m., sheriff's Lt. Scott Ybarrondo said.

The bandit was described as a thin man in his 20s, wearing a blue polka-dot shirt. He told a teller he had a firearm, though none was seen. He fled with an undisclosed amount of cash to the south, towards the Vista Courthouse, Ybarrondo said.

Administrators at nearby Breeze Hill Elementary School kept pupils inside their classrooms for about 90 minutes as a precaution while deputies searched for the robber, who remained at large in the late afternoon. The robbery took place in a shopping center near Route 78 and Melrose Drive.