JACKSONVILLE, Fla. -- A water spout over the St. Johns River witnessed by thousands of people Friday afternoon briefly came ashore in Riverside as a small tornado, according to the National Weather Service.

Several trees were downed near Stockton and Post streets by what the NWS confirmed as an F0 tornado. Two of the trees were blown onto vehicles.

The funnel cloud and water spout moved from Mandarin up the St. Johns River, through downtown and north toward Nassau County between 5 and 6 p.m., knocking out power to thousands of homes. Associated downpours flooded streets in San Marco and Riverside, and lightning from the system caused at least two house fires.

"Thing just was absolutely incredible developing and I watched it until it dissipated," motorist James Thompson told WOKV.

A trained NWS spotter first reported a funnel cloud about 5 p.m., eight miles southeast of the University of North Florida.

Moments later, a Department of Transportation camera at Interstate 95 University showed what Channel 4 meteorologist Richard Nunn determined to be a water spout as the funnel moved over the river. The slow-moving twister could be seen from the camera on Channel 4's Southbank tower for nearly 10 minutes.

The NWS said the funnel was intermittently over the river for about five miles between the Buckman Bridge and Riverside. Nunn estimated that the funnel was visible in some form for at least 40 minutes.

Two other trained weather spotters reported the funnel cloud moving north over the river from Ortega toward downtown at 5 mph.

"Kind of dipping down into the river, it went back up. It went back down into the river and then finally it went back up," Jason Doyle said.

Wires are reported down in San Marco and Lakewood and pea- to dime-sized hail was reported from Mandarin.

A transformer blew on Cedar Street, causing wires to arc and start a fire. Channel 4's Jennifer Bauer and photojournalist Matt James, who were along Cedar Street to cover the storm, were trapped in their car for 30 minutes. The fireball was so intense that it left a 3-foot hole in the ground.

Power outages of up to 8,000 homes were reported, but the JEA had most power restored before the end of the evening.

Police closed the Hart and Fuller Warren bridges due to weather issues, but they were reopened by 6:15 p.m., the same time the tornado warning for Duval County expired.