An unknown hacker is being blamed for setting off all 156 emergency sirens in Dallas, Texas on Friday night.
The alarms are used to warn city residents of severe weather. Dallas is located in a part of the US known as “tornado alley”.
The alarms began wailing at 11.42pm on Friday. City officials were able to reset the system at 1.17am Saturday but only after the system had gone through 15 cycles of 90-second activations.
"It does appear at this time it was a hack, and it does appear this came from the Dallas area," Sana Syed, the city's director of public information, said at a Saturday news conference. However, she didn't wish to say more about the incident for fear of giving away information that might lead to a copycat attack.
The FBI sought to assure residents – thousands of whom called the 911 emergency services hotlines – by tweeting that the emergency sirens were malfunctioning and noting there was no bad weather or active emergency afoot.
Dallas mayor Mike Rawlings used the event to call for more funding of the city's critical infrastructure.
“This is yet another serious example of the need for us to upgrade and better safeguard our city's technology infrastructure. It's a costly proposition, which is why every dollar of taxpayer money must be spent with critical needs such as this in mind. Making the necessary improvements is imperative for the safety of our citizens,” he wrote on Facebook.
Meanwhile authorities continue to investigate the source of the attack.