A man offers prayers in front of the main entrance of Okawa Elementary School where 74 of the 108 students went missing after the March 11, 2011 tsunami. Pic: AP.

TOKYO (AP) — Japan is marking the third anniversary of a devastating earthquake and tsunami that left nearly 19,000 people dead or missing, turned coastal communities into wasteland and triggered a nuclear crisis.

In Tokyo, Prime Minister Shinzo Abe and Emperor Akihito will speak at a memorial service Tuesday to mourn for the victims, marking the moment the magnitude 9.0 earthquake struck.

(MORE: 3 years on: Events, questions mark Fukushima anniversary)

Japan has struggled to rebuild tsunami-hit communities and to clean up radiation from the meltdowns of Fukushima Dai-ichi nuclear power plant. Reconstruction plans are finally taking shape, but shortages of skilled workers and materials are delaying the work.

About 270,000 people are unable to return home, many of them from Fukushima, due to radioactive contamination.