ST. PAUL (AP) -- Officials in Minnesota say a third-party vendor performing work on a 911 system caused a widespread service failure in Minnesota, and that the outage affected North Dakota and North Carolina too.

Several cities and counties scrambled to broadcast backup emergency phone numbers during the hour-long outage Wednesday afternoon. Telecommunications company CenturyLink, which operates 911 networks in the three states, said Thursday it's investigating the causes.

Dana Wahlberg, director of Minnesota's Emergency Communications Networks, says some callers were still able to reach emergency services during the interruption. The department is reviewing how many emergency centers were affected.

CenturyLink Spokesman Frank Tutalo says a third-party vendor's work affected service. He did not immediately return messages seeking comment on the vendor and the scope of the outage.