The death toll in Texas from tropical storm Beryl has risen from three known fatalities to at least six, officials confirmed Monday evening.

Three people were killed in Montgomery County due to falling trees from the storm, according to Chief of Staff for Montgomery County Judge Mark Keough.

One man riding a tractor on a public roadway was killed when a tree fell on him and a couple was killed in a wooded area when a tree fell on them, according to Keough.

The three previously confirmed deaths included two from falling trees and one from drowning.

As of Monday evening, Beryl was designated as a "tropical depression" by officials, due to its sustained winds of 35 mph.

Beryl is moving northeast at 16 mph, continuing to gain speed as it weakens.

Texas Lt. Gov. Dan Patrick said at a Monday press briefing that 2.7 million people across the state are still without power and 10 transmission lines are down.

It will take "several days" to restore power, Patrick said, and the priority will be first restoring it in hospitals, nursing homes and the homes of people that depend on respirators or medical devices with failed generators.

Officials urged members of the public to stay inside and not drive.

Three people have been confirmed dead, two from falling trees and one from drowning.

A third person in the U.S. has died due to tropical storm Beryl, Houston Mayor John Whitmire announced early Monday evening.

The man, who was a civilian employee of the Houston Police Department, died after driving into flood conditions on the way to work Monday morning. His body was retrieved from a submerged car.

The victim has not been publicly identified, and no other details were given about him. His family is currently being notified.

As floodwaters from Beryl rushed through the streets, crews carried out 47 high water rescues across Harris County, which encompasses Houston, Harris County Judge Lina Hidalgo told reporters.

Street flooding is still significant Monday afternoon, Hidalgo said, and she urged residents to stay home.

In terms of storm surge, Hidalgo said, "Things turned out a little bit better than we expected."

Beryl's rough winds have caused more than 2 million customers to lose power across the state. Hidalgo said there will be a clearer picture Tuesday on the timeline for power restoration in Harris County.

In Sugar Land, Texas, just outside of Houston, Beryl has dumped 5 to 10 inches of rain and knocked out power to most of the population, according to Mayor Joe Zimmerman.

"The hurricane passed almost right over us," Zimmerman told ABC News Live.

But he added, "We were ready."

"We had activated our emergency operations center yesterday at noon. We had staff on two, 12-hour shifts, and that staff was able to keep everything up and running," he said.

"It was a considerable wind event. We've got trees down, we've got branches down, we've got inlets clogged up," the mayor said. "But we've got crews out there, we've got our public works crews out there, police, fire, EMS, everybody's available. I think Sugar Land weathered the storm as well as we could."