Japanese authorities admitted they may have been over-zealous in issuing their first major tsunami alert in more than 15 years for a wave that ended up causing almost no damage.

"The agency's tsunami forecasts turned out to be a bit too big. I'd like to apologise for the prolonged alerts," Yasuo Sekita, the Meteorological Agency official in charge of earthquakes and tsunamis, told a news conference.

Authorities yesterday ordered more than half a million people to evacuate seaside areas and predicted that the tsunami sparked by Chile's massive earthquake might top three metres (10 feet) by the time it reached Japan.

When other Pacific-Rim nations had sounded the all-clear, Japanese officials were still issuing warnings, as television stations provided non-stop live coverage with their cameras focused on the calm ocean.

When the tsunami arrived yesterday afternoon, it was just 30 centimetres high. Waves up to 1.2 metres high later inundated some port areas, but caused no injuries or major property damage.

One disaster prevention expert, Hirotada Hirose, said he feared that "warnings by the disaster prevention authorities are losing credibility among the people".

Cautious to the end, Japan's Meteorological Agency maintained its last regional tsunami alerts until 10:15 am (0645 IST) today, after tens of thousands of people had spent the night in evacuation shelters.

Meanwhile scientists have defended warning after tsunami nonevent The warning was ominous, its predictions dire: Oceanographers issued a bulletin telling Hawaii and other Pacific islands that a killer wave was heading their way with terrifying force and that "urgent action should be taken to protect lives and property."

But the devastating tidal surge predicted after Chile's magnitude 8.8-earthquake for areas far from the epicenter never materialised and by yesterday, authorities had lifted the warning after waves half the predicted size tickled the shores of Hawaii and tourists once again jammed beaches and restaurants.

Scientists acknowledged they overstated the threat, but defended their actions, saying they took the proper steps and learned the lessons of the 2004 Indonesian tsunami that killed thousands of people who didn't get enough warning.

"It's a key point to remember that we cannot end the warnings. Failure to warn is not an option for us," said Dai Lin Wang, an oceanographer at the Pacific Tsunami Warning Center in Hawaii.

"We cannot have a situation that we thought was no problem and then it's devastating. That just cannot happen." Hundreds of thousands of people fled shorelines for higher ground Saturday in a panic that circled the Pacific Rim after scientists warned 53 nations and territories that a tsunami had been generated by the massive Chilean quake.