Emergency 911 service to Hamilton’s police and fire departments mysteriously went down early Sunday morning — resulting in dropped calls from two residents.

A city release said the fire department experienced an “outage of incoming emergency calls” around 12:15 a.m., but a dispatcher was initially able to continue taking calls from a backup location at Hamilton’s central police station.

Another unexplained outage followed, however, knocking out 911 service to Hamilton police around 2:50 a.m. That forced both local police and fire to switch to contingency dispatch services from the Halton Police Service — a backup plan that took about 30 minutes to kick in.

Two 911 calls were dropped in the intervening time lapse. Police spokesperson Catherine Martin confirmed those callers were contacted later, but she could not immediately say what the calls were about or if the callers required police assistance.

No fire calls were missed or dropped.

Technicians restored fire department emergency lines around 5:30 a.m., and Hamilton police were back online by 7:31 a.m., Martin said.

Martin said police are investigation the cause of the outage as a “technical matter” and city spokesperson Mike Kirkopoulos said officials have no reason to believe anyone purposely tried to interfere with the emergency call system.

“It is anticipated that a further diagnostic analysis may reveal why the staggered service interruptions (occurred)” he said, adding the first priority Sunday is to “ensure all systems are operating normally.”

Police are reminding residents if they ever encounter a busy signal when calling 911, they can call the main police number at 905-546- 4925.

Work on electrical systems accidentally knocked out 911 service to police last fall for about an hour. There are about 20 calls per hour to Hamilton’s 911 service.