00:48 Sioux Falls Tornado Rips Apart Building in Newly Released Footage Newly released footage from inside a health center in Sioux Falls shows the damage done by an EF-2 tornado that struck the city one year ago.

The governor of Texas has declared a state of emergency in nine counties after widespread, deadly flooding hit Monday morning. Rainfall came down at rates as high as four inches an hour, flooding waterways at rapid rates and leaving residents trapped in their own homes and vehicles.

At least five people have been confirmed dead. According to the Houston Chronicle, Harris County Judge Ed Emmett confirmed four dead in the county. Waller County officials say one person was killed there. The Houston Police Department is also investigating possible deaths, but has not released details on how many.

(MORE: Widespread Flooding Ravages Texas, in Photos)

The number of people killed was expected to rise as first responders assessed the situation.

In Harris County alone, more than 1,000 homes were flooded, according to Judge Ed Emmett. Harris County officials reported nearly 900 water rescues in the city of Houston alone and 1,222 total early Monday afternoon.

"When you get off the freeways and off the main thoroughfares, you could be in water 10 to 15 feet deep," Fire Department spokesman Jay Evans told the Associated Press. "You do not want to trap yourself in these vehicles."

Near Brookshire, Texas, citizens rescued semi truck driver Ron Bumpus from his rig after he drove into floodwaters.

During a tense live broadcast on The Weather Channel, truck driver Daniel Sieczkarski swam out to the vehicle, which was submerged up to the door handles, with a rope. Several other citizens hauled Sieczkarski and Bumpus back through the swiftly flowing water.

Rainfall totals of 10 to 20 inches have been measured in southeast Texas to the northwest of Houston as of 6:30 a.m. CDT, according to the Harris County Flood Control District.

In some places, rainfall rates of 3 to 4 inches per hour were reported. Authorities said there were at least 650 residential calls for help Monday morning as the floodwaters rose.

More than 100,000 customers lost power in the Houston metro area due to the flooding, according to the Houston Chronicle.

"This is a mind-boggling situation," said Jim Cantore, storm tracker for The Weather Channel.

More than 70 horses were rescued and moved to higher ground in northeast Harris County Monday morning. In video shared with KTRK, several horses could be seen struggling for survival as flood waters swirled around them.

As of late Monday afternoon most of the horses had been rescued and none were in serious danger, KTRK reported.

(MORE: Dangerous Flooding Expected To Continue)

Residents were urged by authorities to stay home and off the roads as the flooding worsened, but in some areas, houses were being flooded as well. At one point Monday morning, emergency officials said as many as 60 water rescues were underway simultaneously as rescue workers plucked people from their homes. The National Weather Service in Houston said there were more than 70 subdivisions flooded in the metro area.

Before 5:30 a.m. CDT Monday morning, George Bush Intercontinental Airport had already reported 8.85 inches of rain since midnight, the wettest April day on record there. More than 400 flights into and out of the airport were canceled by 10:30 a.m. CDT Monday morning, according to the flight-tracking website FlightAware.

The City of Houston activated its Emergency Operations Center Monday morning to assist with this life-threatening situation. Most schools in and around the Houston area will be closed Monday in an effort to keep children and their educators off the dangerous roads.

This is a developing situation; please check back frequently for updates.