Japan is marking the fifth anniversary of the devastating earthquake and tsunami that left more than 18,000 dead or missing.

A minute's silence will be held across Japan at 2:46pm (5:46 GMT), the time the quake hit.

Prime Minister Shinzo Abe and Emperor Akihito will offer flowers at a memorial ceremony in Tokyo.

The magnitude-9.0 quake struck offshore, creating a vast water surge that devastated Japan's north-east.

It also triggered the world's worst nuclear disaster since Chernobyl in 1986, after the tsunami knocked out power to the Fukushima Daiichi nuclear plant, taking cooling systems offline, which set off a series of meltdowns.

The subsequent disaster spewed radiation over a wide area and forced the evacuation of more than 160,000 local people. Most of them have not been able to return to their homes, despite extensive decontamination work.

After the nuclear disaster all nuclear power plants were ordered offline, and only a few have since been restarted. The tragedy will also be marked by anti-nuclear protests with many Japanese left with a lingering distrust of nuclear power.

The government has spent billions of dollars on reconstruction work, but much remains to be done.

Takagi Tsuyoshi, Japan's minister of reconstruction, promised the job would be completed.

"Rehabilitation and reconstruction have reached a certain level in terms of 'hardware', but there is still a lack of 'software'. We will attend to both aspects in the future, and achieve total reconstruction within the next five years." he promised.

Overall 470,000 people were evacuated from the area in March 2011, and many residents have since made lives elsewhere.

Where are we now?

--180,000 people have not returned home, of which 100,000 are Fukushima evacuees.

--As of 12 February 174,000 people were still living in temporary, rental or other housing as evacuees.

--Nearly 800,000 tons of tainted water is stored in more than 1,000 tanks at the Fukushima plant. No concrete plans have been made to dispose of the water.

--The government-set time frame for intensive reconstruction will be over at the end of this month.

For many survivors though, emotional difficulties are their main concern.

"Infrastructure is recovering, hearts are not. I thought time would take care of things," Eiki Kumagai, a volunteer fireman who lost 51 colleagues in Rikuzentakata, told Reuters.

"I keep seeing the faces of those who died... There's so much regret, I can't express it."