The 7.2-magnitude quake on January 17, 1995, sparked a major review of quake preparedness in the island nation that suffers about one fifth of the world's most powerful tremors.

Mourners observed a moment of silence before dawn at 5:46 am, the exact time that the quake -- Japan's second deadliest since World War II -- struck the port city.

"Whenever I see someone who looks like one of them, I feel it might be one of them," a man who lost his mother and sister in the disaster told public broadcaster NHK.

"I've been living like this for 30 years," he said.

The quake buried residents in thousands of flattened buildings and uprooted highway overpasses and train tracks, while fires raged through collapsed timber houses.

Heavy damage to the busy harbour area dealt a severe blow to Kobe's economy, sparking a population exodus over the following months and years.

Japan experiences more than 1,000 earthquakes every year. The vast majority are harmless but occasional large ones can still cause enormous damage and loss of life.

In 2011, a 9.0 magnitude quake triggered a huge tsunami that smashed into the northeast coast, killing around 18,000 people and sparking the world's worst nuclear catastrophe in a generation.

The Ishikawa region is still struggling to recover from a huge New Year's Day earthquake last year that killed around 500 people and destroyed houses and infrastructure.

- 'Megaquake' -

This week, government scientists marginally increased the probability of a vast "megaquake" along the undersea Nankai Trough over the next 30 years to 75-82 percent.

Such a jolt could potentially have a devastating 8-9 magnitude, trigger colossal tsunamis, kill several hundred thousand people and cause billions of dollars in damage, experts say.

Over the past 1,400 years, megaquakes in the Nankai Trough have occurred every 100 to 200 years, according to the government. The last one hit in 1946.

Despite the ever-present danger and frequent emergency drills, authorities face a constant struggle to maintain public awareness and readiness for a major jolt.

A recent NHK survey among 1,269 people who experienced the Kobe quake showed that over 60 percent of respondents think "the memories and lessons are fading".

"We need to pass on experiences and lessons to the future also with participation by younger generation people who were born after the quake," said Motohiko Saito, the governor of Hyogo Prefecture where Kobe is located.

Emperor Emeritus Akihito and Empress Emerita Michiko attended a memorial ceremony in the city, one of several events that took place throughout the day.

The couple on Thursday met with people who experienced the disaster and Akihito told one of them "it must have been very hard," private national broadcaster TBS reported.