Tropical Storm Harvey, downgraded from a Category 4 hurricane, is continuing to drench Texas and Louisiana today, with parts of southeast Houston getting more than 40 inches — nearing an all-time U.S. tropical cyclone rain record.

Catastrophic and life-threatening flooding continues in southeastern Texas and portions of southwestern Louisiana, the National Oceanic and Atmospheric Administration said this morning.

The death toll had climbed to 18 after a family of six, including four siblings ages 6 to 16 who were trying to escape in a van, were engulfed by the floodwaters, The Associated Press reported.

“We know in these kind of events that, sadly, the death toll goes up historically,” Houston police Chief Art Acevedo told The Associated Press. “I’m really worried about how many bodies we’re going to find.”

Officials said on Monday that more than 6,000 had been rescued in Houston since flooding began — 3,000 by police and 3,000 by the Coast Guard, which was getting more than 1,000 calls an hour.

FEMA said more than 30,000 people had sought refuge at shelters and it expects more than 450,000 disaster victims to file for assistance. As of Monday night, about 135,400 were without power, down from the 220,000 consumers without power during the peak of the outages on Saturday, AEP Texas said.

Harvey may have set a new U.S. rainfall record for any tropical storm or hurricane as it continues to soak the upper Texas coast and Louisiana, worsening the record-breaking, catastrophic flooding, according to The Weather Channel.

A Coast Guard video depicts a boat rescue next to a truck submerged to its headlights in floodwaters.

A rain gauge near Friendswood, Texas, reported a four-day total of over 48 inches through early this morning.

If confirmed, it would be the heaviest storm total rainfall from any U.S. tropical cyclone in records dating from 1950, topping the 48-inch storm total in Medina, Texas, from Tropical Storm Amelia in 1978, according to research by NOAA’s Weather Prediction Center meteorologist David Roth.

In Harris County, which encompasses Houston, officials said the storm’s catastrophic flooding has led to upwards of 2,200 water rescues, The Weather Channel said.

Swollen waterways are prompting evacuations in surrounding areas. New mandatory and voluntary evacuations were ordered Monday morning in Fort Bend County, Texas, southwest of downtown Houston, over fears and expectations that water levels in the Brazos River will reach record levels, threatening to overtop local levees and inundate homes and businesses.

The NOAA National Hurricane Center expected Harvey to begin a path north late today or early Thursday as a tropical depression.

A storm surge watch has been posted along the Gulf Coast from Houston to the eastern part of Louisiana.

A Coast Guard MH-60 Jayhawk helicopter crew from Air Station Houston rescues five people from floodwaters in a southeastern Houston neighborhood on Sunday.