MELBOURNE, Australia (AP) — Authorities fear a second landslide and a disease outbreak are looming at the scene of Papua New Guinea’s mass-casualty disaster because of water streams and bodies trapped beneath the tons of debris that swept over a village. Thousands are being told to prepare to evacuate, officials said Tuesday.

A mass of boulders, earth and splintered trees devastated Yambali in the South Pacific nation’s remote highlands when a limestone mountainside sheared away Friday. The blanket of debris has become more unstable with recent rain and streams trapped between the ground and rubble, said Serhan Aktoprak, chief of the International Organization for Migration’s mission in Papua New Guinea.

The U.N. agency has officials at the scene in Enga province helping shelter 1,600 displaced people. The agency estimates 670 villagers died, while Papua New Guinea’s government has told the United Nations it thinks more than 2,000 people were buried. Six bodies had been retrieved from the rubble by Tuesday.