Two Ontario men are on their way to Houston to help a family member who has been forced from her home by flooding in the hurricane-battered city.

Bill Hamilton and Pat Quirk left Guelph, Ont., on Monday night after buying an extreme terrain vehicle capable of driving and floating on water, and are on their way to Quirk's sister.

The pair plan to pick up Quirk's sister from the hotel where she has taken refuge, check on her home, and work out a plan to find her a safe place to stay.

Hurricane Harvey made landfall along the Gulf Coast on Friday night as a Category 4 storm and moved northeast along the Texas coast over Houston. The storm has dumped more than 76 centimetres of rain in parts of Texas and authorities have rescued thousands of people left stranded by the storm.

Quirk's 47-year-old sister, who has lived in Houston for a year, was initially stuck in her Houston home, where the ground floor had flooded, Hamilton said. She was helped from her home by a passing motorist and taken to a hotel, but staff have warned guests that the building will likely lose power soon, Hamilton said.

Quirk's sister sent her brother pictures of the hurricane's aftermath early Monday, Hamilton said. Those photos alarmed Quirk and made the 52-year-old decide to go to the city to help his sister, Hamilton said.

When Quirk called Hamilton to tell him of his plan, Hamilton, a 47-year-old landscaper, said he wanted to help out.

"It kind of hit close to home with his sister being there, so I thought I'd give (him) a hand," Hamilton said in a phone interview as he and Quirk made their way to Houston in a pickup truck.

By early Tuesday afternoon, Hamilton said he and his friend were driving through Arkansas, and expected to be in Houston late Tuesday.

"We're in contact with (Pat's) sister now and trying to make a plan as to what part of the city we head for first," Hamilton said.

With numerous streets in and around Houston flooded, Hamilton and Quirk decided to head to the city well prepared for the conditions.

Quirk, a retired banker, bought a $25,000 extreme-terrain vehicle from a snowmobile dealership south of Guelph just for the trip, Hamilton said.

"It'll go pretty much anywhere," said Hamilton, noting that the vehicle can get through mud, rocky terrain, or even across a lake.

While the pair are heading for Quirk's sister, Hamilton said they'll try to help others who need a hand if they can.

"I'm thinking we'll probably be home by the weekend, but who knows?" Hamilton said.

On Tuesday, a pair of 70-year-old reservoir dams that protect downtown Houston and a levee in a suburban subdivision began overflowing, adding to the rising floodwaters from Harvey that have crippled the area after five consecutive days of rain that set a new U.S. record for rainfall for a tropical system.

Forecasters expect the storm to linger over the Gulf before heading back inland east of Houston sometime Wednesday. The system will then head north and lose its tropical strength.

With files from the Associated Press.