In pictures: Houston overwhelmed by 'unprecedented' floods

AFP/GettyWater is so deep in places in Houston that it almost reaches signage over roads

AFPMuch of the city's road system has been overwhelmed by floodwaters

AFPMany shelters have been set up, including at a convention centre

AFPOfficials say 30,000 people are expected to be housed in these emergency shelters

AFPScores of vehicles are submerged across the city, with some owners having to be freed by emergency workers

ReutersThe coastguard has been among the rescuers working to help stranded residents

ReutersHelicopters had to winch people up to evacuate them to safety

ReutersMany evacuees prioritised rescuing their pets above their belongings

ReutersEmergency 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 become

ReutersA woman and her dog awaited assistance on a floating airbed

AFPAt a news conference, the Federal Emergency Management Agency called on ordinary citizens to "get involved" in the unprecedented rescue efforts