Paris - Traditional May Day union marches turned violent in France on Monday and presidential election front-runner Emmanuel Macron attacked far-right rival Marine Le Pen, highlighting the divisions days before the runoff.

Six police officers were hurt in clashes in Paris between masked youths throwing Molotov cocktails and riot police who responded with tear gas, as tens of thousands of union activists took to the streets.

Interior Minister Matthias Fekl condemned the violence and said one officer was seriously burned on the hand while another had serious burns to the face.

Reacting to the scenes, far-right presidential candidate Le Pen tweeted: "This is the sort of mess ... that I no longer want to see on our streets."

In a speech, Macron told thousands of his supporters he would defend "free democracy" if voters choose him on Sunday after Le Pen had urged voters to reject "the world of finance, of arrogance, of money as king" she said.

This time, with left-wing candidates eliminated in the first round, the left is deeply divided over the choice between Le Pen's 48-year-old daughter and Macron, a 39-year-old former investment banker.

Abstention

In Paris's Place de la Republique, 28-year-old teacher Camille Delaye held a placard that read: "Abstention is a political act" - meaning he is so disgusted by both candidates, he will not vote on Sunday.

But Nastassja Naguszewski, 28, who works in local government, said: "You have to put Le Pen as low as possible. One of them is a candidate who will uphold republican values and one is not."

Meanwhile, in the United States, tens of thousands across the country held largely peaceful protests on Monday against President Donald Trump's immigration and labor policies, despite a small pocket of violent unrest in the Pacific Northwest.

Police shut down a protest in Portland, Oregon, that they said had become a riot, after marchers began throwing smoke bombs and other items at officers. Police said they made more than two dozen arrests as a group of anarchists wearing black bandannas and ski masks grew unruly, reportedly breaking windows at businesses, setting fires on downtown streets and damaging a police car.

Despite the West Coast clashes, most nationwide protests were peaceful as immigrants, union members and their allies staged a series of strikes, boycotts and marches to highlight the contributions of immigrants in the country.