A third-party vendor performing work on a 911 system caused the nearly hourlong service failure across Minnesota on Wednesday, officials said.

The widespread outage, which occurred shortly after 4 p.m. and lasted about 50 minutes, disrupted emergency lines to first responders in cities, county sheriff's offices and at the Minneapolis-St. Paul International Airport. It also affected services in North Dakota and North Carolina, said Dana Wahlberg, director of the Emergency Communication Networks Division for the state Department of Public Safety.

The vendor, West Safety Services, was completing a routine process on their network at the time of the outage, according state officials.

CenturyLink, the state's 911 service provider, and West Safety Services are reviewing the incident to determine what triggered the outage.

"CenturyLink is working with the vendor to understand the root cause and preventive measures," Frank Tutalo, a company spokesperson, said in a statement.

West Safety Services could not be reached for comment Thursday.

In response to the system failure, dozens of local public safety agencies immediately posted alternative emergency numbers on social media. Dispatch centers reported that some calls and texts to 911 during that time were received successfully, while others were not, Wahlberg said.

CenturyLink is required to investigate and explain any outage within 14 business days, though Wahlberg said the company has been asked to accelerate its investigation.

"We expect that CenturyLink will review every factor and will provide us with a full reason for the outage," she said.

The state is investigating how many people were affected and to what extent.

From Jan. 1 to June 30, Minnesota's 102 dispatch centers had received more than 1.4 million calls. That averages out to about 7,800 calls per day statewide, suggesting a few hundred calls could have been placed during the 50-minute service failure, a Department of Public Safety spokesperson said.

As of Thursday afternoon, Wahlberg said no dispatch center had reported any serious incidents as a result of the outage, which she called "very, very unusual.

"I'm not aware of another issue like what happened yesterday," said Wahlberg, who has worked in the public safety sector for 30 years.

In April 2014, a nationwide 911 outage affected emergency call centers in seven states. Only about 70 calls in Minnesota were affected at that time, Wahlberg said, and all were concentrated in the metro area.

Wahlberg said she received e-mails Wednesday from colleagues in Louisiana and Ohio around the time of the outage, indicating the disruption could have been more widespread than initially reported.

The Federal Communications Commission was made aware of the disruption and will conduct an independent investigation, which could result in a fine, Wahlberg said. CenturyLink was penalized $16 million for the 2014 outage.

CenturyLink has been the state's 911 service provider for seven years and is under contract for three more.

"We expect our 911 system to be reliable and dependable. And as such, we hold our vendors accountable for that," Wahlberg said. "911 is a vital service — not only in Minnesota, but across the nation."

Katie Galioto • 612-673-4706