Ten thousand people flocked to Sydney's Coogee Beach for an impromptu dance party on Christmas Day - but after the crowds were gone, piles of rubbish remained.

A local woman walked by the beach and decided to make an effort to clean up the mess.

Hours later, Cynthia Colli had picked up 8,000 glass bottles.

'I just couldn't go to sleep thinking about it,' Colli, 35, told Daily Mail Australia.

Thousands flocked to Sydney's Coogee Beach for an impromptu dance party on Christmas Day - but after the crowds were gone, piles of trash remained

The Christmas Day revellers left the beach as quickly as they arrived - but the rubbish they left behind took hours to clean up

Sydney's Coogee Beach resembled a landfill after the Christmas Day party was over

Crowds filled the popular beach on Christmas Day - but after the people were gone, rubbish remained

A local woman walked by the beach and decided to make an effort to clean up the mess

'Disgusting!' wrote a person who posted this photograph to social media. Coogee Beach is pictured in the aftermath of the Christmas Day festivities

'I just couldn't go to sleep thinking about it,' said Cynthia Colli, who helped collect thousands of bottles from the beach

The cleanup effort took three hours and resulted in 20 bags filled with glass bottles and plastic cups

Though messy, the Christmas Day festivities at Coogee were relatively peaceful.

Even as police estimated the massive crowd at 10,000 people, cops made only three arrests for anti-social behaviour.

A police spokesperson said officers were 'generally pleased' with the behaviour of the Coogee Christmas revellers.

The New South Wales ambulance service was called to the beach 20 times during Christmas Day. Paramedics treated six patients who suffered traumatic injuries, three people who overdosed, as well as a number of patients with light injuries.

One person was injured by a bottle and transported to Prince of Wales hospital at 10.10pm, according to an ambulance spokesperson.

In the aftermath of the party, Ms Colli helped a crew of council garbage collectors to pick up the glass bottles, as well as piles of plastic cups.

While the glass containers were still in the sand, the garbage truck couldn't move through without crushing them, Ms Colli explained.

'I spoke to one of the garbage collectors who has worked here for 15 years. He said he's never seen it that bad,' Ms Colli said.

A group of young men, who had emptied a few bottles of alcohol themselves, offered to help her after they saw her toiling in the sand, Ms Colli said.

Some fishermen also offered to clean up the area where they were sitting.

Cynthia Colli with some of the bags that she, with the helping hands of a few others, collected after a Christmas Day rave on Coogee Beach

'You can walk past a problem, or you can stop and do something about it,' Ms Colli said

Together, Ms Colli and her helpers filled 20 trash bags with around 400 bottles in each.

The effort took three hours, and Ms Colli didn't leave the beach until 2am.

'I think there's a nice lesson in there... You can walk past a problem, or you can stop and do something about it,' Ms Colli said.

Ms Colli said she was inspired to take action to keep beaches clean after she was challenged by a friend. Together, the two have started an environmental initiative, called F***giving.