Supporters join to pay respects to slain leader and launch official party campaign.
Thousands of people massed around Benazir Bhutto's tomb in southern Pakistan to mark the end of the 40-day mourning period for the slain opposition leader.
The day of Muslim prayers and rituals also signals the launch of campaigning by her Pakistan People's Party (PPP) for elections on February 18, with her widower Asif Ali Zardari set to deliver a keynote speech.
Many mourners spent the night in tents outside the huge white Bhutto mausoleum in the rural village of Garhi Khuda Bakhsh, listening to mourning songs on tape recorders and reciting verses from the Koran.
"We have to win this election - in our leader's words, democracy is the best revenge," mourner Nabi Bux Kalhoro told AFP.
Party officials said they expected tens of thousands of people to turn out to mark Bhutto's "chehlum" - the completion of the mourning period following her assassination on December 27.
The two-time former premier was killed in a gun and suicide bomb attack in the garrison city of Rawalpindi.
The government has accused a tribal warlord with links to the Taliban and Al-Qaeda of masterminding her murder, but Bhutto wrote before her death that government and intelligence figures were plotting to kill her.
Police said there would be heavy security for Thursday's ceremonies, including a cordon around the raised platform at the mausoleum from which Zardari is due to address the crowds.
"We have made maximum security arrangements on the occasion," said Ghulam Rasool Dombki, police chief of the nearby town of Larkana, the Bhutto family's constituency in southern Sindh province.
"We are also erecting scanners in the area and no one would be allowed to come close to the security cordon without strict checking," he said.
Pakistani authorities have warned that politicians are at risk of further attacks in the run-up to elections. Many have dismissed it as a way of keeping parties opposed to President Pervez Musharraf off the streets.
Despite the warnings and heavy security the area around the mausoleum was already full of people on Wednesday night, with visitors including women and children erecting tents outside and sitting around fires to keep warm.
People had come in groups and caravans mainly from across southern Sindh and central Punjab provinces, but with others from as far north as Pakistan Kashmir.
"We spent three days to reach here on foot from Jamshoro," a city 320 kilometres (210 miles) south of Larkana, said Mushtaq Ali, a diehard party supporter.
Supporters also gathered in Larkana and in the adjacent village of Naudero, where the Bhutto family ancestral home is located.
The PPP has said it will officially begin campaigning from Thursday for the polls, which were delayed by six weeks after Bhutto's death and have so far seen none of the raucous electioneering that is customary in Pakistan.
With the party reportedly riven by divisions following the killing of its charismatic yet dominating leader, it began earlier this week to try to coalesce support behind Zardari by making public Bhutto's will.
The document names him as her political heir, dispelling rumours that she had actually picked their 19-year-old son Bilawal Bhutto Zardari over her husband, who has been hit by unproven corruption charges.
Bilawal was later chosen by the party as co-chairman but Zardari is acting as regent while the young man finishes at Oxford University.
Party officials quoted by state media said Bilawal would not be attending the ceremony because of his studies.