Houston - Massive flooding unleashed by deadly monster storm Harvey left Houston - the fourth-largest city in the US - increasingly isolated on Sunday as its airports and highways shut down and residents were rescued from their inundated homes by boat.The city's two main airports suspended all commercial flights and two hospitals were forced to evacuate patients. A local television station also was knocked off the air.At least three people have been killed so far, with reports of other fatalities still unconfirmed. As night fell, dramatic rescues - sometimes by volunteers with their own boats - were still taking place.READ: Rescuers pluck hundreds from rising floodwaters in HoustonThe National Hurricane Center called the flooding "unprecedented" and said the storm, which crashed ashore late on Friday as a huge Category 4 hurricane, would move into the Gulf before doubling back midweek, bringing even more rain.US President Donald Trump, who had said he did not want to disrupt emergency efforts with a visit, is planning to head to the disaster zone on Tuesday, the White House announced.'Crazy'Rising waters from Harvey inundated roads throughout the Houston area, affecting every major freeway and hamstringing efforts to move people to safety."It's crazy to see the roads you're driving on every day just completely under water," said Houston resident John Travis.Another city resident, Brit Dreger, said: "It doesn't look like we're going anywhere for a while."Overwhelmed emergency services warned residents to head for high ground or climb onto rooftops - not into attics - so they could be seen by rescue helicopters. More than 2 000 rescues had been made so far.The local ABC affiliate showed the helicopter rescue of a man and his 6-year-son - both named Jeremiah - from the second floor of their home. Each only had the clothes on their back and a backpack."This is all we got," the father said. "We thank God. We thank God."Emergency 911 operators in Houston received 56 000 calls in a 15-hour span - seven times more than in a usual full day."We are going on fumes and our hearts ache for community we serve, but we will not stop," said Houston police chief Art Acevedo.More rainTexas Governor Greg Abbott warned the operation was far from over, given the foreboding forecasts."The number of evacuees is increasing. The number in harm's way will increase also with the rain that is forecast to come," Abbott said, adding that the storm had already inflicted billions of dollars in damage.Houston Mayor Sylvester Turner dismissed the idea that evacuations should have been ordered sooner."You issue an evacuation order and put everybody on the highway - you really are asking for a major calamity," Turner told reporters.Houston proper has a population of 2.3 million people, but the greater metropolitan area has more than six million.The National Weather Service said more than 60cm of rain fell in Houston and nearby Galveston in a 24-hour period. Another 50cm were expected.Roger Braugh jnr searches for his boat is this boat storage facility in Cove Harbour in Rockport, Texas, in the wake of Hurricane Harvey. (Rachel Denny Clow, Corpus Christi Caller-Times via AP)Flooding was expected to worsen as Harvey, the most powerful storm to hit the US mainland since 2005, lingers over the area.Harvey ripped off roofs, flipped mobile homes and left hundreds of thousands of people in the dark on the Gulf Coast, home to some of the country's most important oil refineries.Houston's George Bush Intercontinental Airport and Hobby International, the city's two airports, also stopped all commercial flights.Thousands of National Guard troops joined local police and emergency workers to help with rescues in inundated areas of the city.Oil industryBoats also were being deployed, but more were needed - Harris County Judge Ed Emmett appealed to residents to use their own vessels.One volunteer rescuer told KTRK TV: "Basically, there were a lot of people out here and not enough boats."The Federal Emergency Management Agency (FEMA) said there should be no illusions about the long-term impact."This disaster will be a landmark event," FEMA director Brock Long told CNN, adding it would take "years" to recover. Coastal Texas is home to a large number of oil refineries and a number of major ports.ExxonMobil said on Sunday it had closed its massive Baytown refining complex - the second-largest in the country.US authorities said about 22% of crude production in the Gulf of Mexico, accounting for more than 375 000 barrels a day, was shut down.But Abbott said the oil industry was well prepared."They have the ability to ratchet up back up there quickly," he said on Fox News Sunday, predicting a "one- or two-week downturn".