"The town is flooding," Miller said. "All of our first responders are responding."
The Howard County fire department warned people to stay away and said hundreds of rescuers were converging on Ellicott City from as far away as northern Virginia. Howard County officials announced they were opening an emergency operations centre to manage its response.
Videos taken on Ellicott City's Main Street show boiling brown waters flowing down the street, carrying debris and trash. The waters spilled into doors and windows and twisted traffic lights.
Abigail Conte, 19, was at the Bean Hollow coffee shop in the historic section of the city when the rains began this afternoon local time. She said the staff announced they were closing because of a flood warning.
She left the shop and began to make her way to her car.
"As I was walking outside, the street was becoming a river," Conte said.
She came to an intersection where it became too dangerous to continue. She said she was trapped on the second floor of a building and had moved into a backroom because she was afraid a telephone pole might collapse on the shop.
She said the owners of the antique shop said the basement of the building had flooded.
"It's just flooded," said a woman who answered the phone at A Journey from Junk. "I'm trying to work through my own panic attack."
Before declaring a state of emergency, Hogan activated the state's emergency response, which sends extra rescue personnel to the scene from various state agencies, said his spokesperson Amelia Chasse.
Several nearby counties - including Carroll, Frederick and Washington - sent swift water teams, she said.
Ellicott City sustained severe damage in a July 30, 2016, flash flood that killed two people.
During that flooding, houses along Main Street shook as residents filmed the devastation out their windows.
Some formed human chains to rescue those stranded in their cars as the rising waters roared through the historic downtown. Emergency workers climbed onto roofs and chopped holes into stores to save those trapped inside.
In the 2016 flooding, Joe Blevins, a father of three, was swept away as he climbed with his wife from their flooding car.
