The discovery of Bobbi Kristina Brown, the only child of the late singer Whitney Houston, face down and unresponsive in a bathtub last month is being investigated as a criminal matter, police in Georgia have said.

Authorities in Roswell, a suburb of Atlanta, have been questioning people about the circumstances leading up to the discovery on 31 January at her home, but had not made clear the nature of their investigation.

A family source said Tuesday that media reports suggesting Bobbi Kristina would soon be taken off life support were not accurate. Brown's family previously has said she was fighting for her life.

A candlelight vigil Monday at an amphitheatre in suburban Atlanta drew hundreds of people and prompted expressions of gratitude from family members - despite them having asked for privacy.

"We continue to request privacy in this matter," Bobby Brown said in a statement released through his lawyer, Christopher Brown, on Tuesday. "We thank everyone that supported the vigil for Bobbi Kristina. God is hearing our prayers."

The family's lawyer, Christopher Brown criticised erroneous media reports about her condition while maintaining that details needed to be kept private.

"This is a criminal investigation and the integrity of that process requires silence," he said.

Police have said they responded to Bobbi Kristina Brown's home in reference to a drowning. Her partner and a friend found her unresponsive in the tub and performed CPR until help arrived, police said.

Houston, a six-time Grammy Award winner and actress who battled substance abuse, drowned in a hotel bathtub in Beverly Hills, California, on 11 February 2012. Authorities said cocaine use and heart disease contributed to her death at age 48.

Bobbi Kristina Brown was hospitalised twice with anxiety after her mother's death.

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