911 outage reported across multiple US states

It was not immediately clear what was causing the outages.

Late on Wednesday, officials in South Dakota and Las Vegas said that 911 services had been restored, but they did not say what caused the crucial emergency infrastructure to fail.

Requests for comment from the Department of Transportation's Office of Emergency Medical Services, which houses the National 911 Program, were not immediately returned, nor where those sent to the U.S. Federal Communications Commission.

The Federal Emergency Management Agency also did not respond to requests for comment.

The Department of Homeland Security has warned of increased risks of cyber attacks on 911 services, as they have migrated to digital, internet-protocol based systems.

Several cyberattacks targeting 911 systems have taken down the services in recent years, including a 2017 attack that paralyzed 911 centers in over a dozen states.

The South Dakota Department of Public Safety, Las Vegas Metropolitan Police Department and Douglas County, Nebraska, all reported outages to their 911 services.

Late on Wednesday, the Las Vegas police said their 911 service had been restored, and that everyone who called during the outage had been called back and given assistance.

In Texas, the police department in Del Rio, on the border with Mexico, said on its Facebook page that 911 services were down.

South Dakota's Department of Public Safety said efforts were underway to resolve the issue, without disclosing the cause of the outage.

Authorities also asked people not to call 911 as a test.

(This story has been refiled to correct the spelling of 'protocol' in paragraph 6 and fix a typo in paragraph 10)