The 911 system in Massachusetts has been restored following an outage yesterday afternoon.

However, the cause of the outage that impacted the state is not yet known.

"The Massachusetts 911 system has been restored. The public may now resume calling 911 for emergencies," the State 911 Department said in a statement.

An investigation to determine the cause of the outage is underway.

The outage meant that people were unable to call the number in case of an emergency.

It led state authorities to advise people to call local emergency services contacts instead, providing a range of regional dispatch numbers.

According to local media reports, an alert was sent out to cell phones statewide. The message said: "9-1-1 SERVICES are currently down Statewide. Delays in public safety response may occur. CALL local Public Safety business line directly if you or others are having an emergency."

Even Boston Mayor Michelle Wu acknowledged the outage, noting that "calls are not going through."

In February, parts of the US were impacted when making 911 calls following an AT&T outage.

A widespread 911 outage impacted four US states in April. All of South Dakota and parts of Nebraska, Nevada, and Texas were hit.