Many Alaska residents were mistakenly warned on TV and on the radio Friday morning of a tsunami threat along the West Coast of the United States, from San Diego to Alaska's Aleutian islands.

The alert said at the end of a nearly two-minute long message that it was a test. But not all listeners and viewers received that information, officials said.

The National Tsunami Warning Center said there was no threat. It said the message was a routine test sent at about 7 a.m.

Susan Buchanan, a National Weather Service spokeswoman, said the center's test message was properly coded but somehow re-transmitted in an abbreviated format. That stripped the test coding and caused activation of the Emergency Alert System that sends messages to TV and radio stations.

She said it's not clear why that happened, the agency was investigating and could not immediately provide further details. The tsunami warning center is part of the National Weather Service.

The message was sent just months after a civil defense official in Hawaii mistakenly sent an alert indicating a missile was inbound to the islands, prompting changes in how such alerts were issued. The employee who sent the false alert was fired.

In Washington state, officials said a false tsunami warning earlier this week in Clallam County was the result of a Jefferson County official testing a new cellphone app.

A real tsunami warning in Alaska earlier this year included alerts sent to cellphones, something that didn't happen Friday.

Rosemary Dunn, who lives in Anchorage, said she was more curious than panicked when the warning came through.

"I couldn't find any earthquakes and was really perplexed," she said.

She went online and then discovered the alert was not real.

"They said it was misinterpreted. I'd really like to know what's behind that, who misinterpreted that," she said.

Jeremy Zidek, a spokesman for the Alaska Division of Homeland Security and Emergency Management, said there is a time limit for how long emergency alert system messages can last. This was a longer message, and from reports officials have gathered, the information indicating it was a test was cut off for some listeners and viewers, he said.

He said other Alaskans heard the test information.

Often, the message says it's a test at the beginning. It's not clear why the version heard by Alaskans didn't say it was a test until the end. Zidek said the message Friday was intended to be an internal test message.

Tsunami-vulnerable communities were notified by the state emergency operations center that there was no tsunami warning, the state emergency management agency said.

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Associated Press writer Alina Hartounian in Phoenix contributed to this report.