Haunting video shows Nancy Ng just before she disappears on yoga retreat in Guatemala

Relatives of the California woman who vanished during a yoga retreat in Guatemala have released a haunting last video of her paddling from shore in a kayak — while challenging local authorities who believe she then drowned.

Nancy Ng, 29, of Monterey Park, was seen smiling and waving from a kayak on Oct. 19, shortly before she disappeared while staying near Lake Atitlán, as seen in footage shared with “Good Morning America.”

The Guatemalan prosecutor’s office said that a woman with Ng told authorities that they advanced “approximately two kilometers deeper into the lake, where the missing woman tells” the witness that “she wants to swim.”

“And that is when she drowns,” prosecutors told ABC News, with rescuers saying they found her empty kayak.

However, Ng’s family refuses to believe that simple explanation — claiming it took more than 24 hours for her disappearance to be reported, with others still not telling what they know.

“There are people that witnessed what happened, within the group, that haven’t come forward,” Nancy’s sister Nicky Ng told ABC News in an emotional interview.

“We’re racking our brain as to why they wouldn’t want to come forward and help, if nothing nefarious happened.”

Fire and rescue officials told ABC News that there were reports that Ng was last seen about a half-mile from shore and that her kayak was later found empty.

The FBI has offered resources to help in the search, while the US State Department is monitoring the investigation while in touch with Guatemalan officials, ABC News said.

“My dad … he keeps his phone next to him at night,” the missing woman’s sister said.

“He’s hoping for a ransom call, you know, something that will prove that Nancy might still be alive and that she’s out there, that she’s waiting for us to find her,” she said.

The family has also hired a private search team led by Black Wolf Helicopters owner Chris Sharpe.

“We’ve searched 99% of the lake — that’s was with helicopters, drones, boat crews,” Sharpe told ABC News, adding that the terrain and a lack of information has complicated search efforts.

“For me, this is now becoming a criminal investigation because the witnesses who were there at a material time are not being forthcoming,” he told ABC 7.

The family said Ng, a fitness enthusiast and former Cal State law student, works with special-need kids in the Alhambra Unified School District. 

Her little sister said it was her second year attending the retreat, and earlier spoke fondly of the experience and the beautiful area where she was staying.

“Last year, she woke up every morning just to spend some time there by herself without the group and this year was going to be more exciting because they had planned activities on the lake,” she said.

Ng’s mother, Stephanie Li, told ABC News simply:  “Please help us bring Nancy home.”