A magnitude-5.8 earthquake hit western Montana early on Thursday, the U.S. Geological Survey reported, and people felt the tremor hundreds of miles away.
The earthquake struck five miles (9 km) southeast of Lincoln, Montana, at about 12:30 a.m. local time, the USGS said on its website.
"New experience: woken up by an earthquake. No damage just spooky as heck!" Cole Fawcett tweeted in Crowsnest Pass, Alberta, about 285 miles (460 km) north of Lincoln.
Residents in the U.S. west flooded Twitter early on Thursday with similar experiences.
"My mom woke up and yelled at me and my dad that there was a bear shaking our trailer," Brad Wynder said on Twitter.
No significant damage or injuries had been reported about an hour after the quake.
More than 10,000 reports from those who felt shaking were collected on the USGS website.
Several aftershocks with magnitudes of more than 4 were reported by the USGS. The Pacific Tsunami Warning center earlier reported the quake with a magnitude of 6.0.