UPDATE 6:29p ET: Four people are dead and at least 12 people are critically injured after a duck boat tour bus collided with a charter bus on a Seattle bridge Thursday.

The Seattle Fire Department said on Twitter that 90 firefighters responded to the incident and they had evaluated approximately 50 people.

At least two people are dead and nine are critically injured after a duck boat slammed into a tour bus on Seattle's Aurora Bridge.

According to reports, 50 people were injured. The bridge was closed in both directions following the crash, and the cause remains unclear.

The Ride The Ducks amphibious vehicles are a popular tourist attraction in Seattle.