HOUSTON- The death toll has climbed to seven in Texas amid the "epic and catastrophic" flooding left behind in the southeast part of the state from Hurricane Harvey.

On Monday evening, Houston's Mayor Sylvester Turner confirmed three deaths in Houston.

Four other storm-related deaths occurred in La Marque, Montgomery County, East Montgomery County and the coastal city of Rockport.

Houston, the country’s fourth largest city, has been inundated with flooding as result of Harvey, which made landfall late Friday as a Category 4 hurricane and lingered as a tropical storm over the weekend.

Texas Gov. Greg Abbott has activated the entire Texas National Guard. The total number of guardsmen available to the state is roughly 12,000, and all of them will be used in support of recovery efforts in southeast Texas, according to Abbott.

Abbott told ABC News' "Good Morning America" on Monday that he expects the aftermath of Harvey to be "horrific," leaving a mess that will "take years" to rebuild.