Voters in the capital Lome have characterised the poll as an attempt by "the palm tree" to "uproot the maize."
The maize is the emblem of the Gnassingbe's People's Rally (RPT), and the palm tree is the symbol of the Union of Forces of Change (UFC), the main party of the divided opposition, represented by Jean-Pierre Fabre, a 58-year-old economist.
Gnassingbe, a former mines minister and financial adviser under his father, is seeking a second-term mandate but the opposition dismisses him as a candidate of "a system" that froze development over the past 43 years.
Gnassingbe vowed that this poll will raise Togo to new heights, on the basis of "a state of law".
With the main oppisition party [the UFC] expressing concern over possible electoral fraud, forty international observers were deployed by the African Union, 130 by the European Union and 150 civilians and 146 soldiers by the Economic Community of West African States to oversee the elections.
"If they offer you money (to vote), take it, eat there but vote here," Patrick Lawson, the UFC vice president said during a rally.
"We must all keep in mind that our chosen candidate may or may not be the one chosen by the majority," Taffa Taboin, the head of Togo's electoral commission, said at a press conference on Wednesday.
"We are committed to an election that is just, fair, transparent and without violence that will allow Togo to take its place among modern democracies," he said.
Campaigns for the poll in the country of 6.5 million people ended peacefully on Tuesday.
At the stadium in Lome, a bastion of opposition where 15,000 people gathered, they recalled the "old man's" authoritarian regime, marked by assassinations and violent repression of protests and 38 years of ruling of a country as if it were "private property" which produced "a clan of the rich."
The violence that followed the disputed vote in 2005 left up to 800 dead according to various sources, but the UN put the toll at 400 to 500 deaths.
Yet parliamentary elections two years later were peaceful, raising hopes of an end to Togo's long history of political violence and leading to the restoration of foreign aid.
Voting begins at 0700 GMT and closes at 1700 GMT.