Some Amazon employees this morning are working from home after a possible bomb threat shut down at least one of the company’s main Seattle buildings.

Two sources said at least one office has been affected in Seattle’s South Lake Union neighborhood, where the retailer’s sprawling campus is located. The building we are hearing has been closed by the scare is Day 1 South, which is located on a major courtyard at the company’s headquarters. Day One North is unaffected.

Both Day 1 North and Day 1 South were named after the mantra that it is “always day one at Amazon.”

UPDATE, 2:45 p.m.: Employees were sent this alert at 11 a.m., warning it was not a drill and that the evacuation was indeed due to a bomb threat:

THIS IS NOT A DRILL. All, the Business Assurance Center has received notification of a bomb threat at SEA22 (Day 1 South). Emergency services have responded and at this time determined that a building evacuation is necessary to ensure the safety of all associates. Please proceed calmly and safely to the nearest exit and then coordinate with your manager to account for your safety and to arrange for an alternate work location for the remainder of the day. Additional information is forthcoming. This is not a drill.

Multiple inquiries to Amazon spokespeople have not been returned, but the Police Department’s spokesperson Sean Whitcomb confirmed it is investigating a threat in that area. “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,” he said, in a statement sent to GeekWire.

These types of events can often be hoaxes, so we will continue to update this story as it develops.

UPDATE, 3:24 p.m.: Police officers say they have completed a search of the complex and have not found any indications of a credible threat. Police are investigating to identify the person who left the threatening note.

Shortly before the update, Amazon employees received this message, saying the building was again open:

As you know, we decided to proactively evacuate Day 1 South late this morning out of an abundance of caution. The building has been cleared by the Seattle Police Department and has now returned to normal operations, and there were no impacts to other buildings. Thank you for your patience.

At noon, there were a few police cars outside of the offices, and not many people were on the streets, according to GeekWire reporter Taylor Soper, who is at the scene. Despite an Amazon security officer telling us that “nothing is going on,” Amazon employees are not being allowed into Day 1 South.

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

The evacuation comes during the company’s busiest time of the year, with shoppers placing orders for items in time for the holidays.

At this hour, the area around Amazon’s headquarters is typically very busy, with lots of employees visiting restaurants and standing in line at food trucks located at every corner. Starbucks, which shares the courtyard with the two buildings, also remains open and people are going in and out of the parking garage.

The company’s headquarters can often be the location for disgruntled people to bring up their grievances with Amazon.

UPDATE, 2 p.m.: Seattle police say building security contacted them “after staff found a note inside a bathroom in the Amazon complex, in the 400 block of Terry Avenue N.”

“Out of an abundance of caution, the Seattle Police Department Arson/Bomb Squad and explosive detection dog teams have deployed to the complex to assist in the investigation,” the post says. “Employees have evacuated from the complex as police and Amazon.com security search the area.”

Note: We’ve removed references to any specific protests at the company to avoid any unintended implications.