TOKYO (Reuters) - Thousands of people in tech-savvy Japan swamped the Internet in the hours after a devastating earthquake and tsunami to tell loved ones they were safe, but social networking sites were also flooded with worries about an explosion at a nuclear plant.

At least 1,300 people were killed, media said, and thousands of homes flattened as a huge deluge of seawater swept inland in the north of Japan, engulfing roads, farmland and villages.

When news spread on Saturday of a radiation leak at a nuclear power plant run by Tokyo Electric Power Co (TEPCO), after an explosion at the facility, many messages on social networking sites were panic-stricken.

"Came back home at 8 in the morning after the depressing night...Now, the nuclear power plant has exploded and we might already be exposed to radioactivity," said a 23-year-old female office worker from Tokyo on a Facebook page.

"I just don't know what to do, what's coming next, and will I be alive tomorrow?" she asked.

Elsewhere in the world, from the foothills of northern India to crowded cities in the United States, Japanese on vacation used Twitter, Facebook and the Japanese service mixi to get in touch with family after the disaster knocked out phone lines.

"Can't get through via fone.. but Toru got through Facebook. Thank God for Facebook!" read a status message of a Tokyo resident.

"Yep! It brings down dictators, it reunites loved ones," was one of the comments. Others were not so lucky.

"I still cannot contact with my family and friends after the tsunami," posted a female student from Sophia University in Tokyo. "Information is necessary for me."

Many had reservations about the ability of authorities to deal with the disaster.

"I can't trust TEPCO," said a person with the handlename Tanuki Atsushi on mixi, the Japanese social networking site.

"They should not stop working to limit damage to the public even if this is not going to be a big accident like Chernobyl," said another user named papa.

The nervous reaction online was a response to the firm's chequered past. In 2002, the president of the country's largest power utility was forced to resign along with four other senior executives, taking responsibility for suspected falsification of nuclear plant safety records.

The company was suspected of 29 cases involving falsified repair records at nuclear reactors. It had to stop operations at five reactors, including two damaged in the latest tremor, for safety inspections.

Some vented their anger over the disaster on the government of unpopular Prime Minister Naoto Kan.

"I don't think the shaky DPJ deserve to be called politicians," said one Twitter user referring to the ruling Democratic Party of Japan. "Do you think I will ever support them? No never."

(Editing by Raju Gopalakrishnan)

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