911 services went down in parts of South Dakota, Nebraska, Nevada and Texas

Four states have experienced widespread outages of 911 lines, affecting emergency calls throughout South Dakota and swaths of Nebraska, Nevada and Texas overnight, officials said.

Most lines were down for one to two hours, although services appeared to be gradually restored overnight.

The exact nature of the outage appeared to vary across states — some 911 systems reported problems with calls from landlines, while others said customers using mobile phones were struggling to get through. Some police departments or sheriff’s offices said that 911 callers were receiving a busy signal, and they encouraged people to contact them via non-emergency numbers or by text.

No cause for the service disruption has been publicly identified. However, in Texas, the Del Rio Police Department said the issue was caused by “an outage with a major cellular carrier.” The department did not name the carrier or immediately respond to an overnight request for comment from The Post for further details.

The South Dakota Department of Public Safety tweeted that it was “aware of a 911 service interruption throughout the state.” It urged people to instead text issues to 911 instead and advised people not to test-dial 911.

The South Dakota Highway Patrol later tweeted that “service has been restored on the South Dakota 911 system,” adding: “Our emergency system is fully operational and ready to respond promptly to any situation. Your safety is our top priority.”

The Las Vegas Metropolitan Police Department reported an outage affecting 911 calls from landlines, as well as its non-emergency phone line, on Wednesday evening. It urged people to call from a mobile device so they could be called back, or text 911 instead. About two hours later, it said the phone service had been restored and that “all of the individuals who called during the outage have been called back and provided assistance.”

Meanwhile, the Nevada State Police reported outages affecting emergency services in southern Nevada for about 90 minutes Wednesday night.

In Texas, the Del Rio Police Department said it was “aware of an outage with a major cellular carrier affecting the ability to reach 911. This issue is with the carrier and not the City of Del Rio systems. … If you cannot reach 911 via your mobile, please use a landline or another carrier.”

In Nebraska, officials reported outages in various counties. Officials in Douglas County in eastern Nebraska said “a partial statewide outage of 911 has been reported,” with users “reporting a fast busy signal when calling,” while the Buffalo County Sheriff’s Office urged people affected to call non-emergency numbers instead. In southwestern Nebraska, the Dundy County Sheriff’s Office also directed people to its administrative hotline. It later said both cellular and landline 911 services had been restored.

The outages come amid National Public Safety Telecommunicators Week, which celebrates the work of emergency phone line workers across the United States.

Under normal circumstances, 911 calls are handled by trained public safety dispatchers. Some 240 million calls are made to 911 in the United States each year, according to the National Emergency Number Association. About 80 percent are from wireless devices rather than landlines.

The Federal Communications Commission said Thursday that it was “aware of reports of 911-related outages and we are currently investigating.” The Department of Homeland Security has yet to comment on the latest outages.

In February, outages at AT&T affected more than 1.7 million customers in the United States, impacting 911 centers in California, North Carolina and Texas. The centers asked customers to use a landline for emergency calls or find a cellphone that uses a different carrier. AT&T said the disrupted services were not caused by a cyberattack but by an error made while expanding its network.

Last year, Arlington and Alexandria, Va., also experienced problems with their 911 systems, preventing residents from making voice calls to the emergency line.

In 2014, emergency phone services went dark for more than 11 million people across seven states. The entire state of Washington was disconnected from 911, where 4,500 emergency calls failed to go through during an eight-hour period, according to the chairman of the state utility commission. A study by the Federal Communications Commission later found that a preventable software error was responsible for disrupting the 911 service.