Hong Kong (CNN) The organizers of the large-scale demonstrations which kicked off Hong Kong's months-long protest movement earlier this year returned to the streets again Sunday, in a bid to maintain pressure on the city's government following the success of pro-democracy groups at recent elections.

Hundreds of thousands of protesters all ages began assembling at Victoria Park in Causeway Bay at 3 p.m. (2 a.m. ET) under bright blue skies. Many in the crowd could be seen carrying large banners, bearing slogans such as "Free Hong Kong."

By late afternoon, parts of the city had come to a complete standstill, as crowds attempted to move through the main island to Chater Road close to the main financial hub.

More than 800,000 people participated in the march, according to organizers the Civil Human Rights Front (CHRF), in what appeared to be a resounding show of support for the movement after six months of occasionally violent unrest. The police put the figure at 183,000.

The mostly peaceful event marked the first time since mid-August that a march organized by the CHRF had been granted police approval. The group was responsible for two back-to-back weekend marches in early June, which it estimates drew a combined total of more than 3 million people.

Protesters gather for what organizers hope will be one of the largest demonstrations since the movement began in June.

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