Sydney's nine beaches including Manly and Long Reef closed after mysterious white and grey balls found

Nine beaches in Sydney, including popular Manly beach, were closed to visitors on Tuesday after small white and grey balls of debris washed up on the shores at the height of the summer holiday season.

Northern Beaches Council said it was working on safely removing the matter. Most of the samples of the ball-shaped debris were the size of marbles, with some larger, it said in a statement.

Sydney's ocean beaches, famed for golden sand and clean water, draw tourists from around the globe.

List of beaches closed:

• Manly
• Dee Why
• Long Reef
• Queenscliff
• Freshwater
• North and South Curl Curl
• North Steyne
• North Narrabeen

Authorities said they were working closely with the state's environmental agency to collect samples of the debris for testing.

Last October, several beaches including the iconic Bondi east of downtown Sydney were shut after thousands of black balls appeared on the shores.

An inquiry later found that those balls were formed from fatty acids, chemicals similar to those in cosmetics and cleaning products, as well as hair, food waste and other materials associated with wastewater. According to Randwick Council, the initial reports suggested that those balls were Tar balls, these balls are a hydrocarbon-based pollutant.

The impact of these tar balls poses a great threat to the environment. Coogee Beach is home to various marine species, including sharks and migrating humpback whales.