TOKYO: Japan, one of the world's most earthquake-prone nations, plans to launch a seismic alert system next year to capture early quake movements and issue warnings of more damaging tremors, officials said.

A test version of the system, operating in the northern prefecture of Miyagi since February, was able to sound a warning that a big earthquake would strike the city of Sendai 15 seconds before a 7.2 quake jolted the area on August 16, the daily Asahi Shimbun said.

An official at the Japanese Meteorological Agency said sensitive seismic sensors would be installed at 203 places around the country by March 2006 before the system starts operating.

"While it's true that the time between the warning and a large earthquake striking is quite short, this would allow people to turn off gas stoves or get under a table, while train companies could halt trains," the Meteorological Agency official said.

The sensors detect extremely small earthquake waves, analyse them to predict whether more damaging movements will follow later as well as how big the quakes might be, and then automatically issue a warning.

Although the warnings will at first go only to certain organisations such as train and gas companies, the agency hopes eventually to alert ordinary citizens.

The official said problems still remained, most importantly the difficulty of getting accurate information out quickly.

"Our fastest predictions may still be a bit rough, so there might be differences between the strength of the quakes we predict and the ones that actually hit. This is something we have to refine," he said.

Earthquakes are common in Japan, one of the world's most seismically active areas. The country accounts for about 20 percent of the world's earthquakes of magnitude 6 or greater.

In October 2004, an earthquake with a magnitude of 6.8 struck the Niigata region in northern Japan, killing around 40 people and injuring more than 3,000.

That was the deadliest quake since a magnitude 7.3 tremor hit the city of Kobe in 1995, killing more than 6,400.