Authorities were working late Wednesday to uncover the cause of an hourlong 911 service failure across Minnesota.

The widespread disruption knocked out emergency lines to first responders in cities, county sheriffs’ offices and at the Minneapolis-St. Paul International Airport. Dozens of public safety agencies hastily posted alternative emergency numbers on social media.

Some agencies said the disruption primarily affected calls from landlines.

As of late Wednesday, there were no reports of people going without emergency help during the disruption. “To my knowledge, there were no issues getting [through to] first responders,” said Jon Collins, spokesman for the Hennepin County Sheriff’s Office.

CenturyLink issued a one-sentence statement saying that the cause for the failure remains under investigation.

Widespread 911 outages are rare. In 2015, CenturyLink was slapped with a $16 million fine for a previous 911 failure in Minnesota and other states.

For more than six hours in April 2014, 11 million CenturyLink, Intrado Communications and Verizon customers in seven states could not reach emergency call centers, according to the Federal Communications Commission. Penalties were issued because the failure did not stem from a natural disaster or other unforeseeable catastrophe.

That disruption resulted in 6,600 missed 911 calls, including emergency calls about domestic violence, assault, auto accidents, a heart attack, an overdose and an intruder breaking into a home.

After being fined, Century­Link issued a statement saying, “This outage was caused by a third-party vendor’s equipment failure that had never occurred before, and we worked with the vendor to implement measures to ensure that this type of failure will not happen again.”