A renowned British journalist and a Brazilian indigenous affairs expert have gone missing in Amazonas state's isolated Javari Valley.

According to the Coordination of the Indigenous Organization, journalist Dom Phillips and Bruno Arajo Pereira, an employee on leave from the Brazilian Indigenous National Foundation (FUNAI), have been gone for more than 30 hours.

According to UNIVAJA, satellite data showed the pair's last known location in the So Rafael community early on Sunday morning, when they were supposed to meet with a local leader who never showed up.

Following that, the missing duo planned to travel two hours to Atalaia do Norte, but never arrived, according to the group, which dispatched two rescue teams to look for them on Sunday.

The Javari Valley is a mosaic of rivers and deep woodland that makes access difficult for thousands of indigenous people and roughly 16 uncontacted groups.

Phillips and Pereira are still being sought. The disappearances are being investigated by the Brazilian federal prosecutor's office and federal police, as well as the Navy and state military police, according to Eliesio Marubo, a legal representative for UNIVAJA.

Wilson Lima, the governor of Amazonas, has ordered the deployment of specialized police reinforcements to help in search and rescue efforts.

UNIVAJA reported in a press release on Monday that Phillips and Pereira had received death threats prior to their disappearance.

"We emphasize that in the week of the disappearance, according to reports from UNIVAJA employees, the team received threats in the field. The threat was not the first," the release said.

Although the area is protected by the government, prior incursions by land grabbers, illegal miners, illegal hunters, and illegal fishers have resulted in bloodshed.

According to the Brazilian Public Prosecutor's Office, another indigenous affairs worker, Maxciel Pereira dos Santos, was murdered in the same location in September 2019.

Concerns have been made by news organizations about the disappearance, as well as the dangers of covering illicit mining operations in the area.

The Committee to Protect Journalists (CPJ) posted a tweet on Monday, "CPJ is extremely concerned by reports that journalist Dom Phillips went missing while on a reporting trip in the Brazilian Amazon. We urge Brazilian authorities to urgently step up efforts to find Phillips."

Meanwhile, the Association of Foreign Press Correspondents in Brazil and the Association of Foreign Correspondents of So Paulo have urged on Brazilian authorities to take "immediate action"

Phillips has long been a contributor to The Guardian in the U.K., and the publication's global environment editor, Johnathan Watts, has urged Brazilian authorities to move swiftly.