Pyongyang, North Korea (CNN) -- As a military parade that is billed as the largest in Pyongyang's history began Sunday morning, North Korea's increasingly reclusive leader, Kim Jong Il, made a rare public appearance with his youngest son, Kim Jong Un.
Video from the event showed thousands of military personnel who'd been silent a moment earlier erupt into applause and chanting as the Kims appeared in the capital to start the parade.
The event featured 20,000 military personnel marching in lockstep and huge pieces of military hardware -- including many tanks and missiles -- rolling along the parade route as part of North Korea's celebration marking the anniversary of the country's Peoples' Workers Party.
"It's an annual holiday, but in effect this is an elaborate coming out party for the man who will be the next leader," said CNN's Alina Cho, reporting from the parade, referring to Kim's youngest son.
The parade began in the Kim Il Sung Square, named for Kim Jong Il's father, North Korea's founder.
The United States believes that Kim Jong Un has been tapped to replace his ailing father as North Korea's leader.
Little is known about Kim Jong Un. He is thought to be 27 or 28 and was schooled abroad, believed to be capable of speaking some English and German and possibly some French. He is said to have a fondness for Michael Jordan and James Bond.
In a move that surprised North Korea observers, Kim Jong Un appeared to be wearing civilian clothes instead of his military uniform and medals on Sunday, even though he had been named a four-star general last month.
"This is ... Kim Jong Il trying to make sure that senior military officers are not offended by someone who just got his start," said Gordon Chang, a North Korean expert and columnist for Forbes.com. "It shows he needs to massage this process."
In a rare embrace of the media, Pyongyang invited around 60 journalists from around the world to cover the weekend's festivities, Cho said.
"We were quite hastily invited at the middle of last week," she said. "We knew something big was happening but we weren't entirely sure what."
Cho said that security is tight for the celebrations and that even the news media's government minders are being checked by security personnel -- along with Cho's notebook and pen.
Sunday's parade encompassed units of the three services of the Korean People's Army -- the Korean People's Internal Security Forces, the Worker-Peasant Red Guards and the Young Red Guards -- according to North Korea's state-run KCNA news agency.
On Saturday, Kim and his heir apparent appeared at Pyongyang's May Day Stadium as part of the Arirang celebration, which this year marks the the 65th anniversary of the Peoples' Workers Party. The event featured hundreds of gymnastics and dance performances. Participants spend up to eight hours a day training and preparing for the occasion.
Video of the event showed performers dancing enthusiastically for the crowd in the packed stadium. Kim Jong Il and Kim Jong Un could be seen sitting in a private box removed from the masses, flanked by military officials.
Electricity was on throughout Pyongyang on Saturday, Cho said, an unusual occurrence in power-starved North Korea.
The spare-no-expense celebration will likely be frowned upon by many ordinary North Koreans, Chang said.
"With the North Korean economy trending downwards, with poverty and destitution, there's got be the question of the nature of the regime," he said. "They're going to look at this and say, 'Why don't I have clean water? Why don't I have food? How can they afford all of this?'"
Chinese President Hu Jintao sent Kim Jong Il a congratulatory message Saturday, commending the Peoples' Workers Party for "overcoming difficulties and risks and arduously struggling to continuously make eye-catching achievements in its socialist revolution and construction cause," China's state-run Xinhua news agency quoted Hu as saying.
Hu also praised the relationship between North Korea and China, and pledged to make "it an unswerving policy to continuously strengthen and develop bilateral friendly and cooperative ties."
Kim also received messages of support from the party itself.
The Peoples' Workers Party, along with other government entities, praised the party's creation saying it "has ushered in the greatest heyday in its development, a period of great prosperity in the era of the WPK, demonstrating its invincible might under Kim Jong Il's experienced and tested guidance," according to the state-run Korean Central News Agency.
CNN's Adam Reiss contributed to this report