Dressed in white and waving the Colombian flag, rivers of people marched in Bogota, Medellin, Cali and other cities chanting: "No more Petro."

Petro came to power last August with a raft of proposals to reform health care, pensions and the prison system.

His government has also floated the idea of giving criminals immunity in exchange for laying down arms, similar to concessions made to FARC guerrillas in negotiations that led to a peace accord in 2016 but not an end to violence.

Protesters who likened Petro to Venezuela's deceased socialist leader Hugo Chavez, are against the health sector reforms outlined in legislative proposals the president has presented to Congress.

The Petro government has said it will seek to increase the role of the state in healthcare and reduce that of the private sector.

But the move is opposed by the right-wing opposition and the union of private health sector business owners.

The reforms are likely to pass as Petro's left-wing bloc in Congress enjoys a majority thanks to a coalition with centrist and moderate right-wing parties.

"The streets have spoken, they have spoken in a massive way and they are saying: 'It (the government) is not going to impose a health reform... it is not going to impose a total peace on us'," former vice president Francisco Santos said at a march in the capital Bogota Wednesday.

Santos served under former president Alvaro Uribe, one in a succession of right-wing governments that led Colombia for 200 years until Petro, a former member of an urban guerrilla group, won elections in June 2022.

- 'Trafficker before merchant' -

The president had sent a proposal to Congress to suspend arrest warrants for certain drug traffickers as he seeks ways to end ongoing fighting between guerrillas, cartels and other armed groups over drug and illegal mining resources.

Many in Colombia are opposed to the move, fearing criminals will be let off scot-free.

In Cali in the country's southwest, a protester Wednesday held up a banner proclaiming that the government "puts the trafficker before the merchant, the criminal before the businessman."

On Tuesday, smaller groups of people had gathered for demonstrations in response to a call by the president for marches in support of his plans.

Last year, the Congress approved a law that increased taxes on the rich, another move widely opposed.