A protester holds up the French flag during an nti-government demonstrations in Paris on Saturday. Lucas Barioulet / AFP

Thousands of trade unionists and activists from left-wing parties marched with "yellow vest" protesters through Paris on Saturday to present a united front against French President Emmanuel Macron's latest reforms package.

The Paris march, organised by the militant CGT union, came ahead of the main yellow vest march in the eastern city of Strasbourg, where protesters clashed with police trying to enforce a ban in parts of the city centre.

Veterans of the protests, which have been running for six months now, led off the Paris march.

But in a new development, many senior figures from the radical left marched with them, including Jean-Luc Melenchon, the leader of France Unbowed and one of Macron's most vocal critics.

Welcoming this show of political unity, Melenchon told BFM TV: "It's the first time that there has been a call of this kind, that's to say union organisations, associations and political movements." That in itself made it a political event, he added.

It was a government plan to increase diesel prices and raise taxes on pensions last November that sparked the protests in rural France, which quickly ballooned into a full-scale anti-government rebellion.

But in the early months of the movement, its leading figures resisted attempts by parties on the far left and the far right to hijack their cause for their own ends, as they saw it.

A protester holds a placard reading "Right to inform for Gaspard Glanz" during a demonstration in Paris on Saturday. Lucas Barioulet / AFP

Macron rolled back some of his more controversial measures within weeks of the protests starting and on Thursday announced more measures to help people on low pensions.

For his critics however, this was too little too late − and he is still under fire for refusing to go back on his controversial decision to cut a "fortune solidarity tax" on high earners.

In Paris, Green Party senator Esther Benbassa said she had attended every yellow jacket demonstration since they began in November.

"It's good that today that we are with the CGT, because the people of the left have to be united," she said.

In Strasbourg, police sealed off access to the major European institutions in the city in line with a ban by local officials on demonstrations in parts of the city centre.

The march started peacefully but clashes broke out after police blocked the route of the protesters to the European Parliament building, AFP journalists said. Some protesters threw stones and bottles at riot police, who fired rounds of tear gas.

Earlier, police pushed back a group of activists, some of them masked and dressed in black, who tried to force their way through to the Council of Europe building.

Local officials said around 2,000 people took part in the Strasbourg protest.

The Paris march passed off peacefully, and organisers see it as a dry run for Wednesday's May Day rally that will bring together several unions from different sectors.

A separate Paris march of a few hundred 'yellow vests' protested media coverage of the movement and smaller marches also took place in several other French cities.

Agence France-Presse