An emergency radio station mistakenly warned that a massive, volcanic-caused mudflow was headed from the flanks of Mount Rainier and that listeners in the valley below should rush to higher ground.

The emergency lahar warning was broadcast Wednesday for nearly an hour on the 1580 AM frequency in the suburban Pierce County town of Puyallup.

Authorities had no estimate how many people heard the broadcast on the weak frequency, or how many evacuated.

Nancy Eldred heard it while driving in the Puyallup Valley and called her daughter, Renee Hutchinson, in Tacoma.

"I was in tears," said Hutchinson, whose 17-month-old son, Ethan, was in the car with his grandmother. "I was shaking."

After Hutchinson warned co-workers, about 30 people started frantically calling loved ones. Some called their children at schools in the Puyallup Valley and told them to leave immediately.

Emergency officials in communities around Mount Rainier routinely test the system that would, in the event of a real lahar from the volcano, activate 24 sirens around the valley and broadcast a radio alert.

But on Wednesday, 1580 AM picked up the test signal as real and said the lahar was coming. The prerecorded radio message apparently was triggered by a software error.

Puyallup Fire Chief Merle Frank said the problem should be taken care of in the next few days.