Around 50,000 have arrived in Manchester for the first day of the Conservative Party conference to protest against austerity cuts and NHS changes.
The march set off at midday and passed through the centre of the city. It will end with speeches at a rally in Whitworth Park.
Greater Manchester Police said that the mile long protest was one of the largest they had ever watched over, and that no arrests have been made.
Frances O'Grady, TUC general secretary, said beforehand: “The march and rally will allow thousands of ordinary people to show the government exactly what they think of their policies.
"Austerity is having a devastating effect on our communities and services, with 21,000 NHS jobs lost over the last three months alone.
“The NHS is one of Britain's finest achievements and we will not allow ministers to destroy, through cuts and privatisation, what has taken generations to build.”
A Department of Health spokeswoman said there was “absolutely no government policy to privatise NHS services”.
She said: “The NHS will stay free for everyone, but it's right that patients should get the best service - regardless of who provides it.
"Charities, social enterprises and independent providers play an important part in providing NHS care - and have done for many years - helping give patients more choice of where and how they are treated."
A number of roads have closed for the event, and a revised Metrolink service is running.