Only one lane of traffic could get through during the taxi blockade, as cab drivers slowly circled City Hall.
KOMO Radio reporter Charlie Harger, who was live at the protest, said the scene was a "cacophony of sound, with dozens or more horns honking." He said the area was in virtual gridlock during the blockage.
Taxi drivers have been demanding that the city crack down on the for-hire cars, which they call illegal competition. They say the taxicab look-alikes are breaking the law by picking up passengers in the city.
For-hire cars don't have meters and are only allowed to drive customers who call in advance, but they say many drivers are breaking the rules.
The taxicab drivers earlier delivered a petition with more than 500 signatures to Mayor Mike McGinn's office.
And on Friday, taxi drivers with Teamsters Local 117 delivered what they called a $300,000 citation to the Seattle city government.
"That's what taxi drivers have lost in the last year for the City's inaction," the Teamsters said in a tweet.
The battle between taxicab and for-hire drivers has been going on for some time.
The city only issues a certain number of lucrative taxi licenses, and drivers say the for-hire cars are stealing their business. They want the city to do a better job enforcing the law.
In addition to for-hire cars, taxicab drivers are unhappy about a group of other ride-share startups like Lyft, which is neither a taxicab nor a for-hire car.
For-hire drivers say they shouldn't be chastised for picking up fares from the sidewalk because town cars are also doing it.
The city is in the process of reviewing all its regulations about what's called the personal passenger business.