The top US emergencies official has quit following criticism over the response to Hurricane Katrina. Michael Brown, director of Fema, the Federal Emergency Management Agency, had already been taken off the rescue effort by George Bush, who has just ended a two day tour of the Gulf Coast.It was the president’s first visit to central New Orleans since the disaster struck. Brown will be replaced by David Paulison, a former chief of the Miami fire department. More than 500 people are now known to have been killed across the southern states by Hurricane Katrina. The death toll has been increased by the discovery of 45 bodies at a hospital in New Orleans. It is unclear exactly how they died as the building is said to have been evacuated last week. Authorities say around 40 percent of the city is still flooded.