Bobby Brown has said the loss of daughter Bobbi Kristina Brown at the age of 22 is “unimaginable.”

The R&B star released a statement on Monday after his daughter with the late Whitney Houston passed away at Peachtree Christian Hospice in Georgia on Sunday, about six months after she was found, face-down and unresponsive in a bathtub in her Atlanta home on January 31.

Bobby said: “Krissy was and is an angel. I am completely numb at this time. My family must find a way to live with her in spirit and honor her memory. Our loss is unimaginable. We thank everyone for the prayers for Krissy and our family as we mourn my baby girl.”

Bobbi Kristina Brown
Bobbi Kristina Brown has died aged 22 (Jimi Celeste/AP)

Medical examiners said the initial portion of their autopsy on Bobbi Kristina has found no obvious cause of death or significant injuries.

The Fulton County Medical Examiner’s Office began its autopsy on Monday and said there was no evidence of previously unknown medical conditions.

Authorities say passage of time will make it more difficult to determine how and why Bobbi Kristina died.

The medical examiner’s office says it is ordering lab tests and has issued subpoenas for documents — likely Bobbi Kristina’s hospital records — to help determine a cause and manner of death. The agency says a ruling should take several weeks.

Bobbi Kristina Brown with her late mum Whitney Houston
Bobbi Kristina Brown is the daughter of the late Whitney Houston and Bobby Brown (Dan Steinberg/AP)

Experts said time is definitely an enemy in Bobbi Kristina’s case. Any drugs she might have taken passed from her bloodstream long ago. Physical injuries would have been healing even as she remained largely unresponsive. If police overlooked any physical evidence at Bobbi Kristina’s home after she was hospitalised on January 31, recovering it nearly six months later may be impossible.

The Roswell Police Department in suburban Atlanta is still investigating the events that led to Bobbi Kristina’s death, authorities say. A police report described what happened in the townhome she shared with Nick Gordon as a drowning. However, no one has been charged in the case.