Four wallabies trafficked into Vietnam were on their way to a new home in a mountainous northern province on Friday, as wildlife experts called for tighter regulation of the exotic pet trade.

The animals -- which are not native to Vietnam -- were spotted hopping along in Cao Bang Province, which borders China, earlier this week.

According to state news site VnExpress, the wallabies -- which include three males and one female -- were brought from Australia by traffickers.

They were most likely on their way to China, which has a huge exotic pet trade, wildlife trafficking experts said.

It is unclear whether they were released or escaped.

On Friday, the marsupials -- all of which are healthy and weigh between eight and nine kilograms -- were traveling to their new home, the Hoang Lien Rescue and Conservation Center in Lao Cai Province, northern Vietnam.

"After arriving at the center, the wallabies will be raised in a semi-wild environment, with both indoor and outdoor areas," La Van Toi, director of the center, told AFP.

However, he was sceptical the animals were sourced from Australia's wilds, speculating instead that they came from elsewhere in Asia, where they may have been bred in captivity.

Vietnam too has a growing exotic pet trade, much of which is organized through social media.

ENV says animals are being pulled from nature to meet the demand for "cute" pets, despite the species being undomesticated, unfit for captivity and their wild populations detrimentally affected and even threatened with extinction.

"There needs to be tightening of regulations concerning keeping these animals as pets," Hendrie said.

ENV, a Vietnam-based organization, says it receives reports from members of the public seeing macaques, turtles, otters, birds and other species at residences, business establishments, and online.