British backpacker Amelia Bambridge missing on Cambodian island

Amelia Bambridge's sister Georgie (right) said the family were trying to be strong

A British student who disappeared after a beach party on a Cambodian island has been reported missing.

Amelia Bambridge, 21, who was on her gap year, was last seen in the resort of Koh Rong on Wednesday.

Members of her family, from Worthing, Sussex, flew from the UK to Cambodia where searches of the sea, beaches and jungle have begun.

Ms Bambridge's sister Georgie said the family was in touch with police and trying to stay strong as concerns grew.

Friends reported Amelia's "out-of-character" disappearance after her belongings were found on a beach.

Ryan Harris said "alarm bells started" when she could not be found after the party.

"She always sticks with the group. She never wanders off on her own," he said.

Searches have covered areas of water, beach and jungle on Koh Rong

Mr Harris said Koh Rong was "quite a small island" which someone could walk around in two or three hours.

"You might lose your friend after a night out but you'll see them in 20 minutes or you might see them the next morning," he said.

Mr Harris, who said he was on a neighbouring island with another group at the time of the party, said volunteers had come together to search for his friend.

Ms Bambridge has gone missing on the small Cambodian island

Ms Bambridge had been travelling with her friend Ryan Harris

"People are diving. People are checking the jungles and the beaches," he said.

"Police sent three search teams out, so they're helping as well. It's a whole island thing now. Everyone's looking."

Georgie Bambridge said relatives were distraught by her sister's disappearance.

"She is such a big part of this family," she said.

"We need to be strong and we are trying to be really positive, but it's the unknown."

Ms Bambridge, seen on the left with her mother Linda Bambridge and her sister Georgie, had been to a party when she disappeared

The family told the BBC that Ms Bambridge, who has three sisters and a brother, set off on her trip on 27 September and first flew to Vietnam to meet her Vietnamese father.

They both travelled to Cambodia before she checked into the hostel on Koh Rong.

On the night she disappeared, she had been with friends she had met at the hostel and they went to a party on Police Beach - named after its proximity to a disused police station.

Her sister Georgie said she had spent two years saving and planning for her gap year trip while working at Lloyds bank. Her sisters described her as "meticulously organised".

Ms Bambridge, who is a vegan, has a Highland cow tattoo on her arm

A Foreign and Commonwealth Office spokesman said: "We are assisting the family of a British woman who has been reported missing in Cambodia and are in close contact with the Cambodian police."

The Lucie Blackman Trust, which supports the families of missing people overseas, has put out an appeal on Facebook.

The charity said Ms Bambridge was last seen at Police Beach where she attended a party in the early hours of 23 October, but had not returned to the Nest Beach Club Hostel where she was staying, and there were serious concerns for her welfare.