The lights were turned off Saturday night at some of the best known landmarks in major Japanese cities due to concern for electricity shortage.

According to Kyodo News Agency, the trouble at a Fukushima nuclear plant caused by Friday's massive earthquake prompted calls for electricity savings in Japan.

Tokyo Electric Power referred Saturday to the possibility of limiting overall electricity supplies from Monday by carrying out intentional power outages. Among the options being considered by the company is one to divide its service area into several blocks and stop supplying power on a rotation basis, possibly for three hours a day for one area.

Meanwhile, the operator of Tokyo Tower said the illumination of the tower will be cancelled through Wednesday. Similar decisions were taken with regard to the Tsutenkaku Tower in Osaka, Rainbow Bridge in Tokyo and Bay Bridge in Yokohama, all of which are usually lit up at night.

The quake that devastated parts of northeastern Japan halted the operation of Tokyo Electric Power's Fukushima plant, which has since had to grapple with a nuclear core-melt accident.

On Saturday, an explosion occurred at the No. 1 reactor of the plant, although the company said later there is no damage to the steel container housing the reactor.

Kyodo quoted Japanese authorities as saying that the explosion did not occur at the troubled No. 1 reactor, brushing off concerns that the quake-triggered problem could develop into a catastrophe.

According earlier reports from Kyodo, Chief Cabinet secretary Yukio Edano told an urgent press conference that the operator, Tokyo Electric Power Co.(TEPCO), has confirmed there is no damage to the steel container housing the reactor.

The top government spokesman said TEPCO has begun new cooling operations to fill the reactor with sea water and pour in boric acid to prevent an occurrence of criticality.

TEPCO's Fukushima No. 1 and No. 2 plants have lost their cooling functions after the area was jolted by a magnitude 8.8 earthquake Friday.

Due to failure to cool down the No. 1 reactor at the Fukushima No. 1 plant, radioactive cesium and iodine were detected near the facility Saturday.

The detection of the materials, which are created following atomic fission, led Japan's nuclear safety agency to admit the reactor had partially melted -- the first such case in Japan.