Huge crowds are likely to turn out for his funeral in southern Beirut, just hours after supporters of the ruling March 14 bloc gathered in the central Martyrs' Square.Syrian influence
Leaders in the pro-government bloc have urged hundreds of thousands to take part in the al-Hariri rally to show their rejection of alleged Syrian efforts to regain influence in Lebanon.
Many of those taking part in Thursday's rally carried Lebanese flags and photographs of al-Hariri as well as other politicians and political figures killed in attacks blamed on Syria.
The former prime minister was assassinated in a car bombing on Beirut's seafront in 2005, sparking mass protests and the withdrawal of Syrian troops after 29 years.
"In 2005 you took to the streets to force them out. In 2008 you must do the same so that they don't come back," read messages on billboards around Beirut.
Syria denies any links to a series of killings across Lebanon in the last three years.
Schools and universities were ordered to shut on Thursday, while most businesses were set to close as the government declared a holiday.
Concerns that the two events will spark unrest has prompted foreign embassies to urge their citizens to observe extreme caution and avoid travel in Beirut.Staying at home
Al Jazeera's Rula Amin in Beirut said that many Lebanese would welcome the bad weather, hoping that it would keep the turnnout at the rallies low and reduce the chances of violence.
"Many people are staying at home, worried and just hoping that today passes with out any problems," she said.
"The point that March 14 wants to make here is that they still have support and are willing to fight if necessary."
There has been a power vacuum in Lebanon since November, with opposing political factions failing to agree on a new president and the distribution of key cabinet portfolios.
"Open our parliament, free our government, elect a president now," a banner carried by some of the protesters in Martyrs Square said.
Hezbollah has accused Israel of carrying out the killing of Moghaniyah, which Syria, a supporter of Hezbollah, branded a "cowardly and terrorist act".
"The brother commander Hajj Imad Moghaniyah became a martyr at the hands of the Zionist Israelis," Hezbollah said in a statement.
The Israeli prime minister's office denied allegations that it had played any role in the killing.