Brazilian President Luiz Inácio Lula da Silva and Senator Flávio Bolsonaro remain statistically tied in runoff polls less than a week before the October 4 presidential election, while the leftist incumbent has widened his first-round lead, according to several surveys.

In a potential runoff, Lula and the right-wing Bolsonaro would each receive 42% of the vote, according to a Quaest poll commissioned by Globo. A week earlier, Quaest had Bolsonaro at 42% and Lula at 41%. In the first round, Lula leads with 39% against 34% for Bolsonaro, up from 37% and 33% previously.

A separate BTG Pactual/Nexus poll showed Lula at 46% and Bolsonaro at 44% in a runoff, with Lula ahead by 42% to 37% in the first round. Both surveys have a margin of error of two percentage points, Reuters reported.

If no candidate wins more than 50% of valid votes on October 4, the two frontrunners will face each other in a runoff on October 25.

Bolsonaro, the eldest son of convicted former president Jair Bolsonaro, challenged Lula to attend a televised debate on Globo scheduled for October 1. Two earlier debates were cancelled because the frontrunners refused to take part.

"I'm going to the Globo debate. I'm confirming it here. Let him decide. I want to go and debate him," Bolsonaro said at an event in Goiás state.

"Lula, come debate me because I want to rub the truth in your face and I'm going to show that my project for Brazil is better than yours."

He also urged voters backing other right-wing candidates to unite behind him to try to win outright in the first round.

His US-based brother Eduardo Bolsonaro, a key figure in the campaign, told Argentine outlet Infobae he believed a first-round victory was possible.

"As his support grows daily, I believe Flavio (Bolsonaro) can beat Lula in the first round. This can happen if, in the final week, we manage to talk to Brazilians and encourage them to cast their votes strategically,” he said.

Eduardo Bolsonaro said a Flávio Bolsonaro government would send a delegation to Washington to negotiate a free trade agreement with the US. He also said it would rebuild ties with Argentina.

Polls suggest the economy is one of the main reasons Lula has struggled to pull ahead, despite record low unemployment and easing inflation. Nearly half of Brazilians say the economy worsened over the past year, compared with 19% who say it improved, according to a Quaest poll.

Bolsonaro has made rising prices a centrepiece of his campaign, often contrasting supermarket prices today with those under his father's government.

"The government has achievements it can point to, but voters are asking how much of those gains have made it into their own households," said Felipe Nunes, chief executive of Quaest.

Food inflation has slowed sharply, but years of steep increases continue to strain household budgets. Household debt service, excluding mortgages, reached a record 26.6% of income in June, according to central bank data. The burden has been made worse by Brazil's 13.75% benchmark interest rate.

"All the big figures say that this has been a good government," political analyst Thomas Traumann told Reuters. "The fact is that everyday folks just don't agree with that."

Two weeks before the first round, Lula announced a 15% increase in a flagship welfare programme and an executive order banning online betting from October 6, though polls suggest the measures have yet to shift voter sentiment.

Foreign policy has featured little in the campaign, but the result will decide whether Brazil tilts toward Donald Trump's Washington, and whether it joins a regional rightward shift that has brought conservatives to power across much of Latin America in recent years.

"Brazil does not belong in anyone's backyard," Lula told the opening of the UN General Assembly last week in New York, in remarks aimed at Trump.

Lula advocates multilateral diplomacy and trade with all countries, while Bolsonaro favours a right-wing alliance spearheaded by Washington under the Trump administration. Bolsonaro has said one of his first acts would be to review Brazil's membership of the BRICS group.

"While relations with the US would continue as they are with Lula, it is completely unclear what a Flavio Bolsonaro presidency would mean," former Brazilian diplomat and minister Rubens Ricupero told DW.

"Lula has prestige in foreign policy, while Bolsonaro is completely inexperienced."

Leonardo Paz of think tank Fundação Getulio Vargas said Bolsonaro was unlikely to take an aggressive stance towards China, Brazil's main trading partner, given the farm sector's dependence on Chinese demand.

"The unknown factor with Flavio Bolsonaro is how much pressure the US would exert so that Brazil distanced itself from China and to what extent he would yield to the pressure," Paz said.