Specialist search and rescue teams could be brought in to help look for a British man missing in Vietnam after falling while attempting to climb the country's highest mountain.
Aiden Webb, 22, from Norwich, was climbing Fansipan mountain alone on Friday when he fell, injuring himself.
Girlfriend Bluebell Baughan last heard from him on Saturday morning.
Rescuers think he may have wandered into a valley with a large waterfall and fallen in.
Mr Webb, an experienced climber, began his ascent of the 3,100m (10,300ft) high mountain in the northwest of Vietnam at about 06:00 on Friday.
Miss Baughan, 24, from White Notley, near Braintree, remained in contact with him by phone from the nearby town of Sa Pa.
During the trek Mr Webb fell into a ravine, injured his arm and leg, and lost his way. She last heard from him in the early hours of Saturday, when he agreed she should call in a rescue team.
Mr Webb's phone went dead at about 06:20 local time.
Rescue teams spent Saturday, Sunday and Monday on the mountain looking for him. About 60 people including military police, rangers and local people were involved in Monday's search.
Mr Webb's father Trever Webb, and uncle Michael Webb left the UK on Sunday and arrived in Sa Pa early on Tuesday where they met with the authorities and rescue teams, Miss Baughan said.
"They [the authorities] now fear the reason they haven't found Aiden is because he may have made his way to a valley that has a large waterfall in and has perhaps fallen," she said.
"They are trying to contact capable team members from another town that have the skills and equipment to search down the waterfall."
The family was "pretty distraught, but doing our best to brainstorm and push for as much help as possible" Miss Baughan added.
The Foreign and Commonwealth Office confirmed it was helping to support the family and "working closely with the local authorities leading the search."