SAO PAULO (AFP) - Brazilian President Jair Bolsonaro's disapproval rating passed 50 per cent for the first time, according to a poll published by the Datafolha Institute, marking a new low in the far-right leader's declining popularity.

Bolsonaro's gap to former leftist president Luiz Inacio Lula da Silva ahead of next year's elections also increased from 18 to 21 percentage points.

The percentage of people that consider Bolsonaro to be doing a "bad" or "terrible" job increased from 45 per cent in May to 51 per cent in the poll conducted among more than 2,000 people from July 7-8 and published overnight Thursday to Friday (July 9).

Bolsonaro's approval rating also remained at its lowest mark of 24 per cent, set in May.

His highest approval rating of 37 per cent came in December 2020.

But his popularity started to plummet from January 2021, when the government stopped handing out subsidies to mitigate the economic crunch caused by the first wave of the coronavirus pandemic in the country of 212 million people.

And the fall continued as Brazil entered a second, and more lethal, pandemic wave at the beginning of 2021, followed by corruption allegations surrounding Bolsonaro's handling of the health crisis, which has claimed the lives of 530,000 Brazilians.

In the election opinion polls, Bolsonaro's share increased from 23 per cent in May to 25 per cent, but the uptick fell short of Lula's jump from 41 to 46 per cent.

Former trade unionist Lula, 75, was denied the possibility of running against Bolsonaro in 2018, as he was serving a 12-year graft sentence linked to the Petrobras corruption scandal.

But he was released 18 months later and in March had his convictions quashed on procedural grounds.

The Datafolha poll found the popular Lula would defeat 66-year-old Bolsonaro by 58 per cent to 31 per cent in a second round election run-off - another 4 per cent increase on the difference in May.

Both men have their detractors, however, with Bolsonaro's personal rejection rating rising from 54 to 59 per cent and Lula's creeping up from 36 to 37 per cent.

Bolsonaro is the subject of a senate investigation over his handling of the pandemic, the seriousness of which he repeatedly downplayed.

He's also being investigated by the public prosecutor for allegedly failing to act on an embezzlement tip off regarding coronavirus vaccine purchases.

The opposition is pushing for the chamber of deputies president to open impeachment proceedings against Bolsonaro.