Floodwaters reached the roof lines of single-storey homes on Monday and people could be heard pleading for help from inside as Hurricane Harvey poured rain on the Houston area for a fourth consecutive day.
The US's fourth-largest city was still largely paralysed by one of the largest downpours in American history.
And there was no relief in sight from the storm that spun into Texas as a Category 4 hurricane, then parked itself over the Gulf Coast.
With nearly two more feet of rain expected, authorities worried whether the worst was yet to come.
Harvey has been blamed for at least two confirmed deaths.
A Houston television station reported on Monday that six family members were believed to have drowned when their van was swept away by floodwaters.
The KHOU report was attributed to three family members the station did not identify. No bodies have been recovered.
Police Chief Art Acevedo told The Associated Press that he had no information about the report but said he's "really worried about how many bodies we're going to find".
According to the station, four children and their grandparents were feared dead after the van hit high water on Sunday when crossing a bridge in the Greens Bayou area.
The driver of the vehicle, the children's great-uncle, reportedly escaped before the van sank by grabbing a tree limb.
He told the children to try to escape through the back door, but they were unable to get out.
The disaster unfolded on an epic scale in one of America's most sprawling metropolitan centres.
The Houston metro area covers about 10,000 square miles.
It is crisscrossed by about 1,700 miles of channels, creeks and bayous that drain into the Gulf of Mexico, about 50 miles to the south-east from the city centre.
The flooding was so widespread that the levels of city waterways have either equalled or surpassed those of Tropical Storm Allison from 2001, and no major highway has been spared some overflow.
The city's normally bustling business district was virtually deserted on Monday, with emergency vehicles making up most of the traffic.
Most traffic signals were out and most businesses closed.
Elsewhere, water gushed from two reservoirs overwhelmed by Harvey as officials sought to release pressure on a pair of dams where floodwaters were at risk of spilling around the sides of the barriers.
The move aimed at protecting the central business district risked flooding thousands more homes.
Meanwhile, rescuers continued plucking people from the floodwaters - at least 2,000 so far, according to Mr Acevedo.
At least 185 critical rescue requests were still pending on Monday morning, he said.
Rescuers were giving priority to life-and-death situations, leaving many people to fend for themselves.
Houston's 911 system has received 75,000 calls since Harvey inundated the city, including 20,000 just since late Sunday.
The city normally averages 8,000 to 9,000 calls per day.
The Red Cross quickly set up Houston's George R Brown Convention Centre and other venues as shelters.
The centre, which was also used as a shelter for Katrina refugees in 2005, can accommodate roughly 5,000 people.
By Monday morning, it was already half full.
Up to 20 more inches (51cm) of rain could fall in the coming days, on top of the more than 30 inches (76cm) some places have already seen, National Weather Service Director Louis Uccellini said on Monday.
That means the flooding will get worse in the days ahead and the floodwaters will be slow to recede once Harvey finally moves on, the weather service said.
The amount of water was so unprecedented that meteorologists had to update the colour charts on the weather service's official rainfall maps.
In Washington, President Donald Trump's administration assured Congress that the three billion dollar (£2.3 billion) balance in the Federal Emergency Management Authority's disaster fund was enough to handle immediate needs, such as debris removal and temporary shelter for thousands of displaced residents.
When lawmakers return next week, a multibillion-dollar aid package is likely to be added to their already packed agenda.
Mr Trump planned to visit Texas on Tuesday, accompanied by first lady Melania Trump.
Harvey was the fiercest hurricane to hit the US in 13 years and the strongest to strike Texas since 1961's Hurricane Carla, the most powerful Texas hurricane on record.