In pictures: Houston overwhelmed by 'unprecedented' floodsAFP/GettyWater is so deep in places in Houston that it almost reaches signage over roadsAFPMuch of the city's road system has been overwhelmed by floodwatersAFPMany shelters have been set up, including at a convention centreAFPOfficials say 30,000 people are expected to be housed in these emergency sheltersAFPScores of vehicles are submerged across the city, with some owners having to be freed by emergency workersReutersThe coastguard has been among the rescuers working to help stranded residentsReutersHelicopters had to winch people up to evacuate them to safetyReutersMany evacuees prioritised rescuing their pets above their belongingsReutersEmergency 911 operators in Houston received 56,000 calls over a 15-hour time period - seven times more than during a usual working day.ReutersAerial photographs from the city's high-rises show how overwhelmed Houston's infrastructure has becomeReutersA woman and her dog awaited assistance on a floating airbedAFPAt a news conference, the Federal Emergency Management Agency called on ordinary citizens to "get involved" in the unprecedented rescue efforts'Catastrophic' floods rising in HoustonStorm victims urged to call not tweetHarvey v Katrina: Lessons learned?