Updated at 3:15 p.m. ET: Authorities say they found no bomb after a threat was made at a large Boeing plant in Delaware County, Pa., on Tuesday morning.

A Boeing spokesperson told NBC News that several hundred employees were evacuated from the south campus of the Boeing Plant in Ridley Park, where the H-47 Chinook helicopter is manufactured. Ridley Park is located southwest of Philadelphia.

The evacuations happened between 7:30 and 8:30 a.m. ET, after officials became aware of the threat, The Delaware County Daily Times reported. Bomb-sniffing dogs went through the facility and by 1:40 p.m. ET, authorities were wrapping up the investigation.

According to Ridley Township police, a note was left in a bathroom claiming four explosives were planted inside of one of the hangars, the Daily Times reported.

The employees scheduled to work in the affected area of the plant for the current shift were sent home. Operations were to resume at 2:30 p.m. ET, the start of the next shift.

Tuesday’s threat came on the 11th anniversary of the 9/11 terrorist attacks.

NBCPhiladelphia.com's Kelly Bayliss and Reuters contributed to this story.

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