Damascus has condemned his murder.
The Martyrs Square was packed hours before the funeral service began in the Maronite cathedral at 13.00. Mourners waved the Lebanese flags and those of Christian factions, including Gemayel's Phalange Party.
The service was being broadcast live to those gathered in the square. Women threw petals at the coffin, draped in the national and party flags, as it passed through the throng.
"Get Bashar's agent out of Baabda [presidential palace]"
Crowd at Martyrs Square demonstration
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Many people voiced their anger at Bashar al-Assad, the Syrian president, and his Lebanese allies including Emile Lahoud, the president, and the Shia group Hezbollah.
"Get Bashar's agent out of Baabda," the crowd shouted in reference to the presidential palace.
Mike Hanna, Al Jazeera’s correspondent in the Martyrs Square, said that while there was a sense of sorrow in the crowd, Pierre Gemayel’s life was also being celebrated and that the mass gathering was a statement of intent.
He said that people in the crowd, which included a large number of young people who may not have many memories of Lebanon’s 15-year civil war, are determined in their cause to achieve a Lebanon free from all outside influence.
Calls for new president
After the funeral service a series of speeches were delivered from leading political figures including Pierre's father, Amin, Saad al-Hariri, the leader of the March 14 coalition and son of the murdered former prime minister, Rafiq al-Hariri, and Samir Geagea, head of the Lebanese Forces.
Amin Gemayel called for a new president in his speech.
"Unity will not happen until a complete change takes place, a change which will happen from the head down. An election for a new president for Lebanon. We will inform you in the next two days of how we will do this," Amin said.
Rula Amin, another Al Jazeera correspondent in Beirut, said the funeral is being deliberately politicised and engineered into a mass show of support.
Hezbollah officials said the group would take no action in the coming days to allow emotions to cool, but they accused the anti-Syrian parliamentary majority of capitalising on Gemayel's murder for political ends.
Hussein Khalil, political adviser to Hezbollah leader Sheik Hassan Nasrallah, said: "We were on the verge of taking to the streets. The government coalition was in an unenviable position and was in a very big impasse. They needed blood to serve for them as kind of oxygen to give them a new life."
Walid Jumblatt, the Druse political leader and senior anti-Syrian figure who has accused Damascus of the assassination, addressed the crowd from behind a bullet-proof glass screeen, vowing: "They will not take away our determination to live ... and to be free."
Still, he said, he was open for a settlement with the government opponents.
"We are for dialogue," he said.
Geyamel’s coffin will then be returned to his home village of Bikfaya for a private service.
In Bikfaya there was still a sense of shock and loss. Bassan Assad, a local resident and member of the Phalange party told Al Jazeera that people in the village and Christian communities "really don’t know how to react".