SAO PAULO, Sept 8 (Reuters) - Brazilian truckers staged demonstrations throughout Brazil on Wednesday, partially blocking key routes in several states and prompting President Jair Bolsonaro to ask the protestors to stand down.

Truckers sympathetic to the president had partially blockaded highways in 16 states as of the late evening, briefly shutting down traffic in two locations, according to a statement from the Infrastructure Ministry.

In the late morning, federal Brazil's highway police (PRF) had reported 53 blockades on federal roads tied to "social and political events, not involving key issues for independent truckers."

Bolsonaro drew tens of thousands of supporters to major cities on Tuesday, including some truckers, using a national holiday to step up his attacks on Brazil's Supreme Court and voting system. Truckers have previously demonstrated this year over high fuel prices.

"Speaking to the truckers out there, who are our allies, these blockades hurt our economy," Bolsonaro said in an audio WhatsApp message sent to truckers' groups and obtained by Reuters on Wednesday night. "They cause supply shortages, inflation and hurt everyone, especially the poorest."

In a separate video WhatsApp message circulating among truckers' groups and obtained by Reuters, Infrastructure Minister Tarcisio Freitas confirmed the authenticity of Bolsonaro's audio.

Wednesday's blockades affected top grain-producing state Mato Grosso, as well as Minas Gerais, where fuel truckers took part in a 24-hour strike beginning on Tuesday.

Blockades were also reported near the port of São Francisco do Sul in Santa Catarina and in Paraná, near Brazil's second-busiest grain port, regional PRF branches said on Twitter.

Brazil's grain exporters association ANEC, which represents global merchants such as Cargill and Bunge, said the blockades were not currently affecting grain shipments to ports.

In a statement, ANEC called the truckers' demonstrations "a concern," and said it is counting on authorities to find a quick solution.

The Brazilian Institute of Petroleum and Gas told Reuters it was monitoring the blockades, but has not reported any impact on fuel supply.

A massive truckers' strike in 2018 ground Brazil's economy to a halt and destroyed the remaining political capital of then-President Michel Temer.

The dynamics of the current demonstrations are quite different, with demonstrators protesting in favor of the government rather than against it, but Brasilia and financial markets follow all movements among Brazil's truckers closely, given the massive impact blockades can have on the nation's economy. (Reporting by Ana Mano and Nayara Figueiredo in São Paulo, Gram Slattery in Rio de Janeiro and Lisandra Paraguassu in Brasilia Additional reporting by Marta Nogueira in Rio de Janeiro Editing by Leslie Adler, Aurora Ellis and Kim Coghill)