Somalia's president of the now expired Transitional Federal Government Sheikh Sharif Sheikh Ahmed
The election is the final stage of a UN-backed process to set up a new administration for the country, whose 25 presidential hopefuls include the current prime minister and president.
The election has been delayed several times – having already missed an August 20 deadline – but international pressure has increased on Parliament to choose a president swiftly.
UN special representative for Somalia, Augustine Mahiga, last week described it as a "historic" election, praising efforts to "move forward to a new more legitimate and representative" system.
Analysts have taken a far gloomier outlook on the process, suggesting it offers little but a reshuffling of key figures and positions.
Somalia has lacked an effective central government since president Mohamed Siad Barre was ousted in 1991, unleashing cycles of bloody conflict that have defied countless peace initiatives.
Ruthless warlords and militia groups including al-Qaeda-linked al-Shabab insurgents have controlled mini-fiefdoms that African Union troops and other forces have only recently started to capture.
President Sharif Sheikh Ahmed, in power since 2009, is one of the favourites, although he cuts a controversial figure with West observers.
Corruption
A UN report in July said that under his presidency, "systematic embezzlement, pure and simple misappropriation of funds and theft of public money have become government systems" – claims Sharif has rejected.
"We have achieved some goals towards improved security with port, airport, bank and other national institutions operating normally," Sharif said in his campaign speech to Parliament on Saturday.
"If you give me the opportunity for the second time to continue my work, the country will achieve more to overcome the current painful situations," he added.
Prime Minister Abdiweli Mohamed Ali, a US-educated economist, is another strong candidate.
"We realised more on peace building, constitutional affairs and good governance in my 14 months of service," he also told Parliament on Saturday.
The new Parliament, whose members were selected last month by a group of traditional elders, will vote in a secret ballot in up to three rounds. Each candidate had to pay $10 000 to enter the race.
'Intimidation and corruption'
Bitter arguments have begun between rival challengers, divided along Somalia's notoriously fractious clan lines, and the UN Security Council has issued repeated warnings of "intimidation and corruption".
"The future of Somalia depends on each and every legislator voting for whomever they believe can best lead their country," Mahiga said. "I encourage them to carry out this sacred trust free from any external influence."
The council has warned of its "willingness to take action against individuals whose acts threaten the peace, stability or security of Somalia".
But Britain's ambassador to Somalia Matt Baugh said last week that both the outgoing president and prime minister had assured him of "their commitment to respect [the] election outcome".
A candidate needs to take two-thirds of the vote to win outright, otherwise the top four candidates will go into a second round, with a third round of the final two. The winner is selected by a simple majority.
The political developments come as African Union and Somali troops make significant gains against the hardline al-Shabab, although they remain a major threat. Ethiopian troops are also battling them from the south and west.
The extremist insurgents last month abandoned the port of Marka, leaving the al-Shabab with two major ports in southern Somalia – Barawe and the rebel bastion of Kismayo – although an international naval blockade has already greatly squeezed maritime access there.
The al-Shabab a year ago abandoned their last fixed bases in Mogadishu, where they have since reverted to guerrilla tactics, claiming a series of suicide attacks and roadside bombs. – AFP