BRASILIA (BBC) -- Millions of Brazilians vote in presidential elections with Luiz Inacio Lula da Silva seeking a second term. Lula, as the president is known, is seeking the 50% of votes needed to win outright victory in the first round.

But his lead in opinion polls narrowed ahead of the vote, amid allegations of corruption and dirty tricks involving his Workers' Party.

His main rival is Geraldo Alckmin, the centre-left, business-friendly former governor of Sao Paulo state.

Since Lula, the first left-winger to hold the country's highest office in 50 years, was elected in a landslide victory in 2001, his welfare programmes have helped him gain strong support among the country's poor.

But his once-commanding lead in the polls has been dented by a series of corruption scandals involving his Workers' Party.

Final pre-election opinion polls showed Lula dipping a little below the 50% of the vote required to avoid a second-round run-off, while Mr. Alckmin's scores had risen a few percentage points to about 35%.

Two weeks ago two men with links to the Workers' Party were arrested carrying $800,000 dollars in cash, which detectives believe was to have paid for a dossier of corruption allegations against the president's rivals.

The scandal led Lula to sack his campaign manager, but has resurfaced over the weekend with newspapers publishing photographs of the wads of banknotes.

Lula denies ever engaging in smear tactics and says he has been let down by party colleagues, but faces an investigation by Brazil's federal electoral court.

It follows controversy last year over alleged bribes for votes in congress, which led to the resignation of the party's leader and several high-level colleagues.

On Saturday, Mr. Alckmin, who is standing for the Brazilian Social Democracy Party (PSDB), said voters should choose him to rid Brazil of "this plague of corruption" and "to have a government that works".