The death toll increased to 25, the Associated Press reported at 4 p.m. Central on Wednesday. That death toll may climb as rescue and relief efforts continue and the city remains under large amounts of water.
FEMA has said it would need volunteers for the next couple of years.
Houston-area waterways flooded by Harvey's rainfall have crested, Harris County flood control official Jeff Linder told Reuters. There are still two reservoirs that are getting close to peak.
As of Wednesday morning, more than 195,000 individuals have registered for assistance. More than $35 million has been provided, FEMA officials announced.
Fifty eight counties are under Texas disaster declaration.
CNN also reports that the US Coast Guard is searching for two civilian rescuers who were swept away after their boar capsized Tuesday night.
Photos: Hurricane Harvey rescue efforts
Harvey made a second landfall near the Louisiana-Texas border on Wednesday, drenching the region with rain that could lead to "catastrophic and life-threatening flooding."
The rainfall that caused a deluge in Texas has ended for the most part in Houston and is moving east, threatening to dump an additional 3-6 inches from southwestern Louisiana into western Kentucky, the National Hurricane Center said.
Before Harvey made landfall around 5 a.m. ET, two people were killed when a tree fell onto a truck in Jackson County, Texas, an area that was "particularly hard hit" by the storm, officials said.
Louisiana has beefed up its emergency resources, doubling up on high water vehicles, boats and helicopters on duty.
Harvey is expected to bring winds of 30-40 mph and a 2-4 foot storm surge along the Louisiana-Texas border.
"We are dealing with a state that has already had a lot of rain this summer, so we are very aware and conscious of the potential for flooding," said Col. Ed Bush, a public affairs officer for the Louisiana National Guard.
Houston Police sergeant on his way to work and a Beaumont mother who was swept by water were confirmed dead on Tuesday.
According to the Associated Press, 33-year-old Joshua Feuerstein of Conroe died when he drove around a barricade and into flood waters.
First responders are loading boat after boat with evacuees, looking for an undetermined number of people who are missing, including six family members whose vehicle was swept away in the floods, and getting ready to face what is hidden under water.
Houston Mayor Sylvester Turner issued a midnight to 5 a.m. curfew until further notice. He tweeted the move is meant to prevent property crimes at evacuated homes.
A glimmer of hope
Five days have passed since Harvey made landfall in Texas and an uncounted number of people are still trapped waiting for aid.
From her home in a northeast Houston suburb, Anike Allen has seen many of her neighbors being airlifted as she slowly runs out of food. While her home is not completely flooded, she's not sure if there's a way out of her neighborhood.
"The water is receding here, but we are not sure if it's going to come back," Allen said.
For the first time since Harvey rammed Houston over the weekend, authorities say the floodwaters that turned the city into rivers, are slowly receding in some areas.
"We are starting to see a glimmer of hope in what has happened," Harris County Flood Control Meteorologist Jeff Linder said in a news conference Tuesday evening. "Things are going to get better."
There's hope, Linder said, but it will be days, even weeks before the massive volume of water -- which is the most rain ever recorded in the contiguous United States from a tropical storm that made landfall -- is completely gone.
'We help each other out'
Volunteers have come the Houston region to lend a hand and their boats.
Tom Dickers is just one of many people who came hauling their boats from Dallas and San Antonio to evacuate people ever since Harvey began pounding the city with rain.
"This is what Texans would do. We help each other out," Dickers said.
At least 9,000 to 10,000 people have been rescued in the Houston region by first responders. Volunteers said they have helped as many as 400 in one day.
Some would just "come crying, just wanting help," said volunteer Bobba Bedri. "I just felt like I had to get more people out, keep going and keep going."