The launch of a SpaceX rocket ship with two NASA astronauts on a history-making flight into orbit was called off with less than 17 minutes to go in the countdown because of the danger of lightning.
Lift-off is rescheduled for Saturday.
The spacecraft was set to blast off Wednesday afternoon for the International Space Station, ushering in a new era in commercial spaceflight and putting NASA back in the business of launching astronauts from U.S. for the first time in nearly a decade.
Ever since the space shuttle was retired in 2011, NASA has relied on Russian rockets to carry astronauts to and from the space station.
NASA pushed ahead with the preparations despite the viral outbreak but kept the guest list at Kennedy extremely limited and asked spectators to stay at home.
Still, thousands jammed area bridges and beaches to watch, many of them not wearing masks or observing the 6-foot social distancing rules.
The space agency also estimated 1.7 million people were watching the launch preparations online.