Authorities on Wednesday approved for the first time an extension to the 40-year operating life of one of the nuclear power plants affected by the 2011 earthquake and tsunami disaster.

The government's nuclear watchdog allowed an extension of up to 20 years beyond the Nov. 28 limit for Japan Atomic Power Co.'s Tokai No. 2 plant in Ibaraki Prefecture.

The move, together with previous operating limit extensions at three other aging nuclear reactors, could undermine the 40-year cap the country applies in principle to nuclear complexes. The Nuclear Regulation Authority had said extension beyond that would be "a rare exception."