One British passenger said the group, held in Peru, was starting to run out of food and water.
Seventy tourists on a river boat in Peru have been detained by an indigenous group as part of a protest against a recent oil spill.
The UK Foreign Office says a “very small number” of British nationals are among those on the boat.
Peruvian, Swiss, American, Spanish and French nationals are also believed to be among those stranded.
The tourists are not thought to have been harmed. They have been held since Thursday morning.
Activists from the Cuninico community released a statement earlier in the week saying that from midnight on 1 November, no boats or vessels would be able to pass.
“We demand that the government talks to the Cuninico community or face consequences – the ultimate responsibility lies with the President of the Republic [Pedro del Castillo]”, the statement read.
One Peruvian passenger on the boat, Regina Mortua, said they were stranded at the mouth of the Cuninico River.
“A few minutes ago the native community decided to take our [tourist] boat close to their town,” she said.
“A few hours ago another boat came for us to board, however it was not possible, because it only transports food…
“They have just informed us that possibly at night they will transfer all the passengers in boats. However, no passenger wants to leave their belongings.”
Another tourist told local TV the group had been fed, but had been told they would be held for up to eight days, if there was no resolution.
The tourists include a one-month-old child and a pregnant woman, she added.
The UK Foreign Office said: “We are in contact with the local authorities and a very small number of British nationals involved in an incident in Peru.”
The oil spill that sparked the protest from Cuninico’s indigenous community happened on 16 September.