Tens of thousands of mourners packed Pyongyang's snowy main square Wednesday to pay respects to late leader Kim Jong-il as North Korea tightened security in cities and won loyalty pledges from top generals for Kim's son and anointed heir.

Women held handkerchiefs to their faces as they wept and filed past a huge portrait of a smiling Kim Jong-il hanging on the Grand People's Study House, in the spot where late President Kim Il Sung's photograph usually hangs.

Kim Jong-il died of a heart attack Saturday, according to state media, which reported his death on Monday.

While the regime appeared stable, Reuters reported that Kim Jong-un, the dead dictator's untested, 20-something son, would have to share power with an uncle and the military, as the isolated country moved to collective rule from strongman dictatorship.

Citing a source with ties in Beijing and the North Korean capital of Pyongyang, Reuters said a military coup is unlikely now that the armed forces have pledged allegiance to Kim Jong-un.

North Korean defectors living in South Korea prepare to fly balloons carrying anti-North Korea leaflets near the border on Wednesday. The slogans on the balloons read: 'Terminate three generation hereditary power transfer' and 'Go to hell, Kim Jong-il.' (Kim Kyung-Hoon/Reuters) In Pyongyang, meanwhile, a huge crowd of mourners converged on Kim il-Sung Square with traditional white mourning flowers in hand. The crowd grew throughout the day, even as heavy snow fell, and some mourners took off their jackets to shield mourning wreaths set up in Kim's honour, just below the spot where he stood last year waving to crowds at the massive military parade where he introduced his successor, Kim Jong-un.

Two medical workers rushed to carry away a woman who had fainted.

"We chose to come here to care for citizens who might faint because of sorrow and mental strain," Jon Gyong Song, 29, who works as a doctor in a Pyongyang medical centre, told The Associated Press. "The flow of mourners hasn't stopped since Tuesday night."

South Korean intelligence reports, meanwhile, indicated Wednesday that North Korea was consolidating power behind Kim's untested, 20-something son, Kim Jong-un.

Worries around Northeast Asia have risen sharply as Kim Jong-un rises to power in a country with a 1.2-million troop military, ballistic missiles and an advanced nuclear weapons development program.

South Korea has put its military on high alert. In another sign of border tension, Chinese boatmen along a river separating North Korea and China told The Associated Press that North Korean police have ordered them to stop giving rides to tourists, saying they will fire on the boats if they see anyone with cameras.

Along the Koreas' border, the world's most heavily armed, South Korean activists and defectors launched giant balloons containing tens of thousands of propaganda leaflets, a move likely to infuriate the North. Some of the leaflets opposed a hereditary transfer of power in North Korea. Some showed graphic pictures of former Libyan leader Moammar Gadhafi's battered corpse and described his gruesome death.

[IMAGEGALLERY galleryid=1604 size=small]

Kim Jong-il ruled the country for 17 years after inheriting power from his father, national founder and eternal North Korean President Kim Il Sung, who died in 1994. Kim Jong-un only entered the public view last year and remains a mystery to most of the world.

Seoul's National Intelligence Service believes the North is now focused on consolidating Kim Jong-un's power and has placed its troops on alert since Kim Jong-il's death, according to South Korean parliament member Kwon Young-se.

South Korean military officials, who spoke on condition of anonymity because of office policies that restrict comment on intelligence matters, confirmed that North Korea has ordered its troops to be vigilant but said that doesn't mean they're being moved.

North Korea announced Monday that Kim had died of a massive heart attack two days earlier at the age of 69 — although some accounts put his age at 70.

Lawmaker Kwon said the NIS has told the parliamentary intelligence committee, which he chairs, that senior military officials have pledged allegiance to Kim Jong-un, and that more security officers have been deployed in major cities across the country. Intelligence officials declined to comment.

According to a Defence Ministry report submitted to parliament Tuesday and leaked to reporters by South Korean lawmakers, some North Korean units conducting winter drills returned to base following the news of Kim Jong-il's death. It also said official mourning events have begun in a number of front-line bases across the country. The report did not elaborate.

Young Kim leads procession

Unification Ministry spokesman Choi Boh-seon said in a briefing Wednesday that the government hasn't spotted particular troop movements in North Korea. Military officials said they also haven't noticed serious developments.

Initial indications coming out of North Korea suggest the transition to Kim Jong-un has been moving forward.

The young Kim led a procession of senior officials Tuesday in a viewing of Kim Jong-il's body, which is being displayed in a glass coffin near that of Kim Il Sung. Publicly presiding over the funeral proceedings was an important milestone for Kim's son, strengthening his image as the country's political face at home and abroad.

State media showed video of Kim Jong-un receiving mourners, including foreign envoys, as he stood near his father's body with an honour guard. He was sombre during the greetings, although footage at one point showed him teary-eyed. A report in the North's official Korean Central News Agency did not specify which foreign countries the envoys represented.

According to official media, more than five million North Koreans have gathered at monuments and memorials in the capital since the death of Kim Jong-il at what state media said was the age of 69 — though some accounts say he was 70.

Hundreds of thousands visited monuments around the city within hours of the official announcement that Kim had died.

The North has declared an 11-day period of mourning that will culminate in his state funeral and a national memorial service on Dec. 28-29.

The propaganda leaflets sent into North Korea on Wednesday by South Korean activists are a sore point with the North, which sees them as propaganda warfare. North Korea has previously warned it would fire at South Korea in response to such actions. There were no immediate reports of retaliation, however. South Korean activists vowed to continue sending leaflets.