Men and women, some singing songs from the days of the country's 1970s liberation war, brought traffic to a standstill as they headed to a football ground in the Highfields suburb where Mugabe addressed them.
In his speech, Mugabe denounced what he called "onslaught" by Britain and its allies.
"We are no longer British territory. Britain has no right to discuss almost every week in their stupid parliament, Mugabe asked, launching a new attack on Britain after it failed to prevent him from being invited to a EU summit next month.
"Have they no sense? Has Britain ceased to have any rationality?"
Gordon Brown, the UK prime minister, said he would boycott the EU-Africa summit in Lisbon after Mugabe confirmed that he would be there.
Supporters of Mugabe last month said they were organising a solidarity campaign of marches and rallies across the country that would culminate in a mass demonstration in support of Mugabe in Harare ahead of the December 11 party convention.
Zimbabwe 'united'Jabulani Sibanda, chairman of the Zimbabwe National Liberation War Veterans' Association, said the march was to "show the world we are united".
"We support our president and he is our candidate in the 2008 elections," Sibanda said on national television on the eve of the march.
"We support our president and he is our candidate in the 2008 elections"
Jabulani Sibanda, War Veterans' Association chairman |
Supporters were ferried in hired buses and trains from across the country while some came in pick-up trucks and lorries.
Military helicopters hovered around the city centre as the march began.
Mugabe thanked the crowds for endorsing his candidacy, vowing that he would not let them down and would continue to defend Zimbabwe's independence.
"Where it comes to Zimbabwe, I will never ever give in. I will not let you down and you will not let me down also," he said.
He also accused multinational companies operating in Zimbabwe of colluding with the West to encourage an uprising against his rule.
"They withhold products to try to make people turn against their government," Mugabe said, accusing some shopowners of making huge profits from overcharging.
Economic crisis Although Mugabe has managed to deter political opponents, analysts say he faces a threat from the economy - seen by the World Bank as the fastest shrinking outside a war zone - because it may spark social unrest.
Some members of the ruling Zanu-PF party have said that the economy and their business interests suffered under Mugabe's leadership and want him to step aside and appoint a successor capable of reviving the economy and improving strained ties with key Western donors.
The country has an annual inflation rate of nearly 8,000 per cent.