The treaty, which came into force in 1970, has been overtaken by a world in which developing nuclear arms has become attractive not only to many countries, but also to "terrorist groups," ElBaradei told Friday's issue of Le Monde.
The number of countries believed to be able to create such weapons "is estimated at 35 or 40," he said.
"And under the current regime, there is nothing illicit for a non-nuclear state to conduct uranium-enriching activities ... or even to possess military-grade nuclear material," he said.
Should any one of them decide to break their commitment to the non-proliferation treaty, experts believe it "could produce a weapon in just a few months."
He added: "We are already on the verge of catastrophe with North Korea."
Elsewhere in the interview, ElBaradei said his agency was at work verifying Iran's nuclear programme, and said a report would be made at the next UN Security Council meeting.
To cope with the increasing risk of other countries developing nuclear arms, the agency head said a beefed-up version of the non-proliferation treaty was needed, beyond the tweaking that it went through in 1995 after the first Gulf War.
"We have to reach agreement on limiting the construction, in civilian programmes, of nuclear material for military ends by confining this to installations under multilateral control."
A "new safety system" that would treat the causes of international insecurity, not just their symptoms, also should be created that would not be based on "dissuasion, but on fairness and universality," he argued.