A bomb threat shut down at least one of the Amazon headquarters' main buildings in Seattle's South Lake Union neighborhood on Monday, according to multiple media reports. Although an ongoing investigation is being carried out, the nature of the threat was not immediately clear.

With evacuations being imposed at Amazon's campus on Terry Avenue, an unidentified employee told Komonews.com, an ABC affiliate, that he had received an email stating that there had been a bomb threat and was instructed to leave the building.

Amazon CEO Jeff Bezos was seen evacuating the building as well, the same employee added.

Another source, who had knowledge of information from three employees, told GeekWire that the threat had kept employees away for the day from the building known as Day 1 South, which is located on a major courtyard at the company's headquarters.

At least one employee, who said they already went home, said there had been no follow-up alert to indicate it was a drill, according to Fox News.

"We are investigating a threats complaint in the 400 block of Terry Avenue North and are working with the affected business. That's all the information I can provide at this time," Seattle police Sgt. Sean Whitcomb said in a statement.