Documents obtained under freedom of information laws reveal for the first time that coal seam gas wells have been drilled directly under suburbs in south-west Sydney.

The documents were obtained under the Government Information (Public Access) Act 2009 by Lock the Gate Alliance, and show homes in Narellan Vale and Mt Annan have active AGL coal seam gas wells drilled directly underneath them.

"I am just totally shocked to discover that there is an active CSG well drilled directly under our neighbourhood," said Narellan Vale resident, Pierre Power.

"I can't believe that we haven't been told about this and that it took a freedom of information request from Lock the Gate to find out what AGL have been up to out here.

"I'm really worried about the health of my children. One of my sons is already getting nosebleeds. Families just shouldn't be put at risk like this by unsafe and secretive coal seam gas mining" he said.

"The information in these documents reveals a desperate lack of transparency and openness from AGL and the NSW Government," said Dan Robins, spokesperson for Lock the Gate Alliance.

"This information should all be out in the open, and the community should be fully informed about the risks they face every day from living above a gasfield.

"Last year this community were alarmed when a nearby well sprung a gas leak. Now they learn these wells have been drilled directly under their homes.

"We're calling on the Premier, Mike Baird, to step in and require AGL to decommission these wells, and to improve the regulations to ensure that there are no wells operating within 2km of residential homes anywhere in NSW," he said.

The documents and maps obtained under the Government Information (Public Access) Act 2009 are available on request