The Baltimore Sun reports that a cyber-attack on the city's network forced the emergency service's Computer Aided Dispatch (CAD) offline.
The CAD system is used by 911 operators to direct first responders – police, fire, and ambulance – to the scene of an emergency.
We're told the attack was directed at a specific server, and took down the CAD system from 8.30am Saturday until around 2am Sunday.
Operators were still able to manually dispatch responders during the outage, albeit much less efficiently.
The attack came at a particularly bad time, as thousands of protesters from the area gathered Saturday in Baltimore and in nearby Washington DC as part of the nationwide march against gun violence.
No systems beyond the one CAD server were hit in the e-assault, and no data was exposed or stolen.