Governor Larry Hogan toured the area and promised "every bit of assistance we possibly can". The Howard County Fire & EMS agency tweeted that water was above the first floor of some buildings at the height of the disaster.
Mr Kittleman said there have been no reports of injuries but added the situation was still developing and more rain is expected.
'This is a catastrophic and life-threatening extremely risky situation, ' the alert warned.
When asked to compare Sunday's flood to the flooding in 2016, Hemmis said, "I'd imagine this is worse".
The town experienced similar flooding two years ago.
The reporter made his way into the town because he was a native, he said. "All of our first responders are responding".
During an evening news conference, Howard County Executive Allan Kittleman said authorities are not aware of any fatalities or missing people.
"We have a deck that goes into the woods, and we knew that was an escape route to Church Road", she said.
She came to an intersection where it became too risky to continue.More news: Are you a Laurel or a Yanny? Explained!
The department tweeted at about 5:20 p.m. that "water is receding".
Many organizations and groups have set up donation calls to help residents and business owners. "I'm trying to work through my own panic attack".
Hogan signed the order while receiving a briefing in Ellicott City from state and local emergency management personnel. Don't come out to look at the flooding.
The Washington Post's Capital Weather Gang reported radar indicated 3 to 6 inches of rain has fallen in just two hours in the Ellicott City area and it continues to rain heavily.
Videos showing muddy water running through the Ellicott City, which has been the hardest hit by the raging waters, have inundated Twitter.
The 2016 flood spurred an influx of giving to rebuild in Ellicott City. Located in the valley of the Patapsco River, a major waterway flowing to Chesapeake Bay, Ellicott City is known for its flood-prone location as much as its historic downtown.
"To say lightning strikes twice is basically what's happening", Halverson said. "To have this happen weeks apart and 30 miles apart is extraordinary".
"They say this is a once every 1000-year flood and we've had two of them in two years", Mr Hogan said, referring to an earlier emergency in 2016.
The aftermath of the floods in Main Street Ellicott City. The body of another tourist, Jessica Watsula, was found under the Ilchester Bridge.