Victory in Monday's election would cap a decades-long effort to rehabilitate the Marcos legacy after the patriarch was deposed and the disgraced clan chased into US exile.
But the prospect of Ferdinand Marcos Jr moving back into the presidential palace has alarmed rights activists, church leaders and political analysts who fear he could rule "without constraint".
Ten candidates are vying to succeed President Rodrigo Duterte in the landmark elections seen by many as a make-or-break moment for Philippine democracy.
The Marcoses' remarkable return from pariahs to the peak of political power has been fuelled by public anger over corruption and poverty that persisted under governments that followed the dictatorship.
Polls indicate Marcos Jr will win more than half the votes, which would make him the first presidential candidate to secure an absolute majority since his father was ousted in 1986.
Analysts warn such an outcome would lead to weaker democratic checks and balances, more corruption and a fresh attempt to overhaul the 1987 constitution -- which could include scrapping the one-term limit for presidents.
"If he wins really big that could give him the kind of confidence and momentum to more radically alter the Philippines political system," analyst Richard Heydarian told AFP.
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