Ben Hammond from the Blacktown Greens said it was about triple the number of people he had expected.

The turn-out, he said, was a show of support against the coal seam gas industry and an indication of the community’s anxiety about it.

Mr Hammond said everyone he spoke to at the rally shared similar concerns.

‘‘A lot of (the talk) was about the rights of landowners and about the water supply,’’ he said.

The technique used to extract gas from coal seams, hydraulic fracturing, or fracking, requires water and chemicals to be injected into the seam via a borehole.

The gas companies AGL and DART Energy have licenses to drill for gas across the majority of the metropolitan and greater Sydney areas.

Both companies have denied they have any current plans to drill for gas in the Blacktown area but signalled that drilling may happen in 2013.

The rapidly-expanding gas industry has attracted criticism from environmental groups, residents groups and the farmers lobby.

Lobby groups, including Lock the Gate Alliance, which represents land owners, The Greens and Sydney Residents Against Coal Seam Gas, have called for the state government to put a moratorium on the industry until there has been an independent public inquiry into it.