The first call was received around 8:30 p.m. It was described as a large explosion of white light, Snohomish County sheriff's spokeswoman Shari Ireton said.
The caller thought it might have been a plane crash off I-5 near the Snohomish-Skagit County line, Ireton said.
The Federal Aviation Administration reported that there were no missing planes.
Similar calls of an unknown light were received by authorities in Skagit County, Ireton said.
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