The collapse occurred while workmen poured concrete on the top floor of the structure. The top five floors at one end slammed down like dominos.
"It sounded like an earthquake. The whole building was shaking," said a pipefitter who was on the second floor of the garage when it caved.
The 10-story garage was to have 2,400 parking spaces. An adjacent 18-story hotel tower also is under construction.
One construction worker injured in the garage collapse previously had fallen through a floor at the site, his wife told the Associated Press.
The worker hurt his ankle in that incident almost a year ago. Two other workers injured then have not returned to work full-time, she said.
"I just think it's a big rush job. That's why all these men are getting hurt and dying," said the wife of one worker.
An incident at the site occurred in October 2002, when workers were injured after a one-story prefabricated panel of concrete they were standing on collapsed.