A tsunami warning was accidentally broadcast in Alaska on Friday, causing confusion among local citizens, officials say. It marks the third mistake this year involving the U.S. warning system.

The incident happened just after 7 a.m. local time when a message from the Emergency Alert System was aired on radio and TV channels in Alaska, advising that a tsunami warning was in effect.

“The National Weather Service has issued a TSUNAMI WARNING for the following counties or areas: Alaska, at 7:02 AM on May 11, 2018,” the message on TV said.

The alert caused confusion among local residents. Jennifer Williams, the news director for KSRM, said the radio station was receiving calls from residents who asked about the warning.

The mistake happened during an internal test to determine transmission times for the dissemination of tsunami warnings, according to the National Tsunami Warning Center. “We are investigating this issue,” the center said.

Friday’s false alert did not affect the entire warning system. The warning was not sent to mobile phones in Alaska and tsunami warning sirens were not activated.

The U.S. warning system has experienced a number of mistakes this year. Most notably, a missile attack warning was mistakenly issued for Hawaii on January 13, causing widespread panic as people sought shelter.

In February, a tsunami warning was accidentally sent through third parties to a number of people along the U.S. East Coast. AccuWeather blamed the National Weather Service for causing the mistake, saying the NWS had coded a test message as a real warning.