Pakistani officials were forced Thursday to repair a leak in its oldest nuclear power plant, lying on the outskirts of its economic hub Karachi on the Arabian Sea coast, an official said.

"An emergency had been declared yesterday after leakage of heavy water was reported," a Karachi Nuclear Power Plant (KANUPP) official told AFP.

KANUPP is the oldest nuclear power plant in the nuclear-armed nation. It is owned and operated by state-run Pakistan Atomic Energy Commission and has been in commercial operation since 1972.

"Our staff controlled the situation after a few hours and the emergency is over," the official told AFP.

"During the emergency no radioactivity was recorded. None of our staff is affected," said the official.

He said the plant had been closed for routine maintenance since October 5.

US cables leaked last year exposed the extent of long-standing American concerns about Pakistan nuclear arms safety, particularly fears that its arsenal could fall to terrorists.

Pakistan has flatly ruled out that possibility.

In May, Pakistan opened a 330-megawatt nuclear power plant at Chashma, in central Punjab province, built with China and said Beijing had been contracted to construct two more reactors in a bid to ease a crippling energy shortage.

Pakistani plans to produce 8,000 megawatts of electricity by 2025 to address an energy shortfall which triggers violent protests each summer.

The nuclear-armed Muslim nation, with a population of 167 million, produces only 80 percent of its electricity needs, starving industry that has slumped in the face of recession and three years of Taliban-linked bombings.