No injuries have been reported in the flood, and by 5:20 p.m. the local fire and rescue department said the waters were receding, according to The Baltimore Sun. The agency added that water had risen above the first floor of buildings in some areas and that it had received reports of building collapses.
Emergency management officials urged people to avoid downtown Ellicott City.
Ellicott City has been rebuilding since the 2016 flooding damaged and destroyed businesses.
Mr. Miller said Sunday's rain started around 2:45 p.m. and had not yet subsided as of around 6:30 p.m.
Two people died as a result.
Jessica Ur, a server at a cafe on the city's Main Street, told The Baltimore Sun she saw the gushing brown waters carry three or four parked cars down the street. Says Hogan: "They say this is a once every 1,000-year flood and we've had two of them in two years".
At least five roads in Baltimore have been closed due to the flooding.
Photos and videos taken by eyewitnesses show floodwaters several feet deep surging down Main Street in the city's historic district.
The newspaper reports that the swirling waters reached the second flood of one building at its height. That's the same street devastated by flash flooding in July 2016.
About 8 inches of rain have fallen in Ellicott City so far Sunday afternoon. However, Howard County officials tweeted that there was "no call for volunteers or unsolicited donations" immediately, but urged people to look for updates on that front. He asks that those in the area stay off roads.
They also say a Flood Warning is effected for Prince George's and Calvert Counties.
The National Weather Service said a flash flood warning has been issued for the area, calling it an "extremely unsafe situation" and urging motorists not to attempt to navigate flooded roads.