WATCH: Torrential rain causes severe flooding in Houston

HOUSTON — Reports of flooding and damage, including three confirmed fatalities, have begun to pour in as now-Tropical Storm Harvey continues to linger over Texas.

Rescuers answered hundreds of desperate calls for help Sunday as floodwaters from the remnants of Hurricane Harvey rose high enough to begin filling second-story homes, and authorities urged stranded families to seek refuge on their rooftops.

Since Friday, some parts of Houston have received as much as 19 inches of rain, with much more on the way, said WFTV meterologist Eboni Deon.

"Some areas can expect to receive an additional foot or two of rain in the next few days," said Deon.

The National Weather Service said some areas of Texas may see up to 50 inches of rain from Harvey.

The National Hurricane Center says torrential rain will continue as Tropical Storm Harvey drifts east-northeastward with very little additional motion expected over the next few days.

Police evacuated two apartment complexes overnight in the Greenspoint neighborhood of Houston, rescuing more than 50 children from rising water.

A tornado touched down in the Houston suburb of Cypress Saturday afternoon, damaging several homes and buildings but causing no apparent injuries.

Marilyn Shaughnessy told the Associated Press she didn't expect the worst of Tropical Storm Harvey to hit the Houston area until Sunday -- only to have the tornado bear down on her house. 

Shaughnessy, a retired police officer, says she had her family run to their laundry room and wait out the tornado. Their house shook and framed pictures fell off the walls.

Watch a Houston hotel lobby flood after heavy rain from the storm

Florida Gov. Rick Scott said the state has sent Twenty-five Fish and Wildlife officers, 17 high-water vehicles, two Mobile Command Centers, eight shallow-draft vessels and four patrol boats.

The Orlando Fire Department said it has sent rescue equipment to Houston as well.

Hurricane Harvey came ashore near Rockport, Texas late Friday evening. With its arrival, people were braced for "life-threatening storm surge, rainfall and wind hazards to portions of the Texas coast."

The mayor Rockport confirmed that at least one person died in the storm.

Harvey was the first Category 4 hurricane to make landfall in the United States since Hurricane Charley in 2004. The storm was downgraded to a Category 1 just before daybreak on Saturday.

Harvey was downgraded to a tropical storm by Saturday afternoon.

Landfall

The massive storm made landfall at 10 p.m. local time as a Category 4 storm, with maximum sustained winds of about 130 mph.

Read: Hurricane Harvey: How powerful is the storm?

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The cities of Houston, Corpus Christi and Brownsville were already experiencing the storm's rain bands.

The slow-moving storm is fueled by warm Gulf of Mexico waters. Forecasters are labeling it a "life-threatening storm" with landfall predicted late Friday or early Saturday between Port O'Connor and Matagorda Bay, a 30-mile stretch of coastline about 70 miles northeast of Corpus Christi.

Millions of people have braced for a prolonged battering that could swamp dozens of counties more than 100 miles inland.

Read: Hurricane preparedness guide

"This hurricane is going to sit over parts of Texas for days and days and days," Shields said. "The flooding will be historic."

As many as 30 inches of rain is expected, Shields said.

Brock Long, the director of the Federal Emergency Management Agency, called the storm a "very serious" threat.

Long said he expects extensive damage from significant rain over the next three days.

Crews across Florida are on standby to help Texas as Hurricane Harvey comes bearing down.

OUC, Duke Energy and FPL have offered assistance to Texas, but have not been asked to respond yet.

Gov. Rick Scott tweeted that he reached out to Texas Gov. Greg Abbott to let him know Florida stands ready to offer resources they may need.

Gas Prices

Harvey is going to cost Floridians more at the pump.

“Typically, with hurricanes like this, we see prices go up just due to increase in demand,” said AAA spokesperson Tamra Johnson. “We also have to look at how Hurricane Harvey will be moving through the Gulf Coast where we do see a large portion of U.S. refinery capacity.”

AAA said to expect a five to 15 cent per gallon increase through the weekend.

But since Harvey is expected to be the most powerful and destructive hurricane to hit the U.S. in more than a decade, the impact could last much longer.

Dozens of crews on oil platforms across the Gulf have already been evacuated by various oil companies and several refineries were shut down ahead of the storm.

The Associated Press contributed to this report.

Cox Media Group