The US Bank branch in downtown Fargo, 505 2nd Ave. N., was robbed just before 11 a.m. today.
Lt. Pat Claus said a man who will be questioned was detained in an alley behind the Hotel Donaldson and Rooters bar.
The bank robbery marks the second in Fargo in six days, following Friday's robbery at Western State Bank at 4301 13th Ave. S. Prior to the pair of recent heists, no Fargo bank had been robbed since Aug. 3, 2009.
At about 11:30 a.m., Claus said detectives had been sent to the bank to begin an investigation.
Signs on the bank's entrances said it was closed due to an emergency. It wasn't immediately clear when it will reopen, but the signs directed customers to the Moorhead branch at 403 Center Ave.
Claus said police got the call about the robbery at 10:56 a.m., and the FBI has been notified. He said more information will be released this afternoon.
Police briefly blocked off the alley where the man was detained, and officers were seen inspecting a bag and canvassing for other evidence.
One witness said officers asked him if he'd seen a man running south through the alley and across First Avenue North, but he hadn't.