Five scuba divers from Britain, France and Sweden are missing in the sea off remote islands in Indonesia after being swept away in a current.
Three of the divers, two women and a man, are British, the Foreign and Commonwealth Office confirmed.
The other members of the group are a Swedish woman and a French man.
They failed to return from a dive yesterday in the treacherous waters of the Komodo National Park in the Nusa Tenggara islands east of Bali, police said.
"A rescue team from the Indonesian police and navy conducted a search this morning for the five missing foreigners but there has been no result so far," said Manggarai Barat district police chief Butje Hello.
The husband of one of the missing British women said the search was being hampered by a lack of fuel for a helicopter which had been offered from Kupang on Timor Island.
"We've got a big search operation happening here but we're having trouble getting aircraft to fly because of fuel problems," said Ernest Lewandowski.
He said he and his wife Kathleen Mitchinson, who own a dive shop on the nearby island of Flores, had been leading two separate groups of tourists on the dive.
He only noticed his wife's group was missing when his group surfaced an hour after they entered the water.
"There were three boats out today searching. I was on a speedboat going around all the beaches and everything to see if they had washed up," he said.
The Foreign Office is providing consular assistance and liaising with the local authorities involved in the search, a spokeswoman said.
The Komodo National Park is a popular diving destination which is well-known for spectacular coral and fishlife as well as strong currents.
"The area is reknowned for big fish, deep water and fast currents," said a UK diving instructor.
"Most of the diving there is drift diving - where you go down in one place, let yourself be taken along by a current, and come back up somewhere else.
"The surface support - the boat they're on - follows them, and normally when a drift dive goes wrong it's either because of diver error - they don't come back up when they're supposed to - or because the surface support hasn't worked."
It is also home to many rare species including the world's largest lizard, the Komodo dragon.