Councillors last night agreed to urgently consider the matter after they were presented with a 406-signature petition from residents requesting the council back the community's call for answers.

Councillor Greg Petty put forward a notice of motion seeking to have the council write to NSW Health asking for it to hold a public information session with concerned residents and have the department liaise with the council on undertaking air, soil and water testing at three sites: the "old quarry" area, the "duck pond" and Helensburgh Public School.

Read Di Young's petition

Read a mother's impassioned letter to councillors

In asking for the support of fellow councillors, Cr Petty described the current heartache and uncertainty in Helensburgh.

"The last few months have been difficult in Helensburgh," he said.

"In March I attended a fund-raiser for a [sick] child, he has subsequently passed away.

"Di Young simply wants to know when she brings [son] Matthew home from hospital each time that the environment she's going into is safe, for him and for everyone else."

MAP: Petition demands cancer cluster answers

Nine-year-old Matthew Young was diagnosed with Burkitt's lymphoma in August.

He is the sixth child in Helensburgh in five years to be diagnosed with blood cancer.

Mrs Young has led a community call for an investigation into the high number of cases.

NSW Health has agreed to set up an advisory panel featuring epidemiological, public health, clinical and environmental specialists to consider any evidence of an unexpected number of cancer cases and any risk factors.

Last night, Cr David Brown revised Cr Petty's motion to have the panel to oversee the testing, rather than put the responsibility in the hands of the council.

"This is simply about delineating the functions we expect the health system to undertake," he said.

"We don't have the experts in this area that the department has access to. I agree we should play a role here to put heat on the health department."

Councillors agreed to the change.