Police in Brazil searched ex-president Jair Bolsonaro's home and seized his cell phone on Wednesday in an investigation into allegations of falsifying Covid-19 vaccination records, an allegation the far-right vaccine skeptic denied.

Bolsonaro, who faced widespread criticism for his unorthodox handling of the pandemic, denied wrongdoing in comments to journalists after the operation, accusing the authorities of trying to "fabricate a case" against him.

"I repeat: I have not been vaccinated," he told reporters clustered in the garage of his home in Brasilia.

"There was no falsification on my part," said Bolsonaro, 68.

"I'm surprised... by the search and seizure operation in an ex-president's home, trying to fabricate a case."

The former president, who led Brazil from 2019 to 2022, defied expert advice on managing the pandemic and joked the vaccine could "turn you into an alligator."

He faced widespread criticism over his handling of Covid-19, which has claimed more than 700,000 lives in Brazil.

Federal police confirmed they were investigating "the insertion of falsified Covid-19 vaccination data" into the health ministry's electronic vaccination records system, but did not mention Bolsonaro by name.

"The falsified entries, which occurred between November 2021 and December 2022, resulted in the alteration of the true Covid-19 vaccination status of the individuals in question," police said in a statement.

"As a result, the individuals were able to emit vaccination certificates and use them to evade health restrictions put in place by authorities in Brazil and the United States."

Bolsonaro left Brazil for the United States in December, after losing his re-election bid to veteran leftist Luiz Inacio Lula da Silva -- a bitterly divisive election fought largely over the far-right incumbent's controversial management of Covid-19.

The US requires international air travellers to present proof of vaccination against Covid-19, a requirement the White House announced on Monday would end on May 11.

The requirement does not apply to foreign government officials -- which was Bolsonaro's case when he arrived there on December 30 last year, the second-to-last day of his presidency.

Police said they were carrying out 16 search and seizure orders and executing six arrest warrants as part of the operation. (AFP)