VIENNA, Sept 20 (Reuters) - Japan needs to do more checks at its earthquake-hit nuclear plant before it can decide when the plant should restart, but damage to the reactors appears to be limited, Japan's nuclear watchdog said on Thursday.

Operator Tokyo Electric Power Co. <9501.T> plans to open and inspect all reactors at the Kashiwazaki-Kariwa nuclear plant, the world's biggest, by early November to determine the damage done in the July quake, a watchdog official said.

"At this moment, we cannot say when the reactor could be restarted," Akira Fukushima, deputy director for safety examination of Japan's Nuclear and Industrial Safety Agency, told journalists in Vienna.

"We are going to open the reactors and then using, for example, cameras (to investigate)," he said. "Radioactive material change in the reactor water is very stable ... so that indicates that there is no big damage inside the reactor."

The plant was hit on July 16 by a quake of 6.8 magnitude, exceeding the worst seismic impact the plant had been designed to withstand.

Inspectors from the United Nation's International Atomic Energy Agency (IAEA) watchdog said in August it could take months, or even a year or more, before the plant could be restarted.

The IAEA said on Thursday it was in contact with the Japanese government about sending another mission to the plant sometime between November and January.

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