Mr Burnham said his changes could save lives
Labour's health secretary has refused to rule out closing hospital accident and emergency departments in London if his party wins the election.
Andy Burnham told BBC London he had a "responsibility" to make changes and it was "not tenable" to have a moratorium on closures.
The Conservatives said it would mean hundreds of thousands of people would lose hospital facilities.
The Liberal Democrats said there was already massive waste in NHS London.
Mr Burnham said: "There is a big review under way looking at services across the capital.
"The proposal was that by making changes in London we could save 500 lives a year. I believe as health secretary I've got a moral responsibilities to make those changes."
Asked if he would rule out closing accident and emergency departments or other hospital facilities, he replied: "I don't believe it's tenable to have a moratorium on all hospital change."
Mike Penning, Conservative health spokesman, said he had seen documents prepared by NHS London proving hospital department closures were under consideration.
He said: "It's not tenable to close A&Es where hundreds of thousands of people are going every year.
"The NHS document said 'oh we'll get them to go somewhere else'. So 70% of people will suddenly have to go to a polyclinic - only eight of which are available."
Mr Penning continued: "People need A&Es - you can't just close them. And the public were not consulted."
Among the accident and emergency departments currently threatened with closure in London are those at Kingston Hospital in south London and the Whittington Hospital in Archway, north London.
Norman Lamb, Lib Dem health spokesman, said: "We are wasting so much money on bureaucracy - the head of London health is earning £250,000 a year.
"We need that to be reemployed in frontline services. They have taken 800 managers in London alone."