Nicole marches across the southeasternmost American state, downing power lines, flooding homes and leaving at least four people dead.

"Structural damage along our coastline is unprecedented," officials say. (AFP)

Hurricane Nicole was downgraded to a tropical storm after slamming into Florida's east coast as a Category 1 storm but not before leaving at least four people dead and causing a path of destruction.

Two people died on Thursday when they were "electrocuted by a downed power line" while driving their vehicle, according to the Orange County Sheriff’s Office.

"We are urging all of our residents and visitors to use extreme caution if they are outside in the wake of the storm today," the sheriff's office said in a release. "Never touch a downed power line. If you are driving and see a downed power line, change directions immediately."

The Florida Highway Patrol said two more people were killed in a storm-related vehicle crash.

Authorities said the driver of a pickup truck lost control of the vehicle on Florida's Turnpike and struck the driver of a tow truck who was standing behind his parked vehicle. Both drivers died in the crash.

"Structural damage along our coastline is unprecedented. We've never experienced anything like this before," county manager George Recktenwald said during a news conference earlier, noting that it's unknown when it will be safe for evacuated residents to return home.

Nicole made landfall just south of Vero Beach with winds of 120 kilometres per hour, destroying homes and buildings, flooding the coastline and leaving more than 335,000 residences and businesses without electricity.

Governor Ron DeSantis said there were 17,000 electricity linemen ready to begin restoring power and that numerous other assets including rescue boats and vehicles will be deployed as needed.

More floods expected

The storm was the first November hurricane to make landfall in Florida in 37 years and only the third on record.

It delivered another devastating blow just weeks after Ian came ashore on the Gulf Coast, killing more than 130 people and destroying thousands of homes.

The storm is expected to weaken to a tropical depression early on Friday and become a post-tropical cyclone.

The National Hurricane Center said that up to eight inches of rain could drench eastern, central and northern portions of Florida through Saturday, causing more flooding.

Flooding is also possible through the southeast US and the central Appalachians, extending northward through eastern Ohio, west-central Pennsylvania and western New York on Friday night into Saturday.

Source: TRTWorld and agencies