A government-sponsored ceremony commemorating the 20th anniversary of the enthronement of Emperor Akihito will be held Thursday at Tokyo's National Theatre of Japan.

During the ceremony, Prime Minister Yukio Hatoyama and others will deliver congratulatory speeches. The emperor himself will respond to the celebration.

At around 9:30 a.m., people began signing their names in registers in commemoration of the anniversary at designated spaces in front of the Imperial Household Agency building in the Imperial Palace. The signing event is scheduled to run through 4 p.m.

Emperor Akihito, 75, was enthroned Jan. 7, 1989, following the death of his father Emperor Hirohito, posthumously known as Emperor Showa.

His formal accession ceremony took place on Nov. 12, 1990 at the Imperial Palace, in front of attendants from home and abroad, after a period of mourning for Emperor Hirohito.

About 50,000 people are expected to attend another ceremony hosted by business organizations and a group of lawmakers in the Imperial Palace Plaza, with popular vocal and dance group Exile performing a new song written for the event.

The Metropolitan Police Department will set up a task force Thursday to oversee security in the capital in relation to the commemoration ceremonies and U.S. President Barack Obama's scheduled visit on Friday.

A total of 16,000 personnel, including some 5,500 members of riot police squads, will be deployed in preparation for possible demonstrations and sabotage by radical groups, as well as for controlling traffic.