At least 50 people died in flash flooding and landslides on the Indonesian island of Flores and in East Timor on Sunday.
Rescuers are still attempting to find survivors, and officials are warning the death toll will probably rise further.
The disaster management agency BNPB said torrential rain sparked widespread destruction, with flood water from overflowing dams submerging thousands of homes.
“On Adonara island to the east of Flores, a bridge collapsed, and rescuers were battling heavy rain, strong wind and waves,” the spokesman said.
In neighbouring East Timor, a two-year-old child was among at least three people killed in a landslide on the outskirts of the capital, Dili, a Reuters witness said.
Officials said on Sunday that another 11 people were killed by flooding in Dili.
“Heavy rains and overflowing water have drowned people’s homes and have also claimed the lives of several victims,” East Timor deputy prime minister José Reis said in a statement.
“There are roads that have collapsed, trees have fallen, and made it difficult to access some areas,” he said, calling the incident the worst in East Timor for 40 years.
Power supplies were cut and the presidential palace was flooded as heavy rain and strong winds have lashed Dili since late on Saturday.
Indonesia’s weather agency said a tropical cyclone is approaching the Savu Straits between the southern part of Nusa Tenggara province and East Timor’s north coast, warning that it could bring yet more rain, strong waves, and high winds.
East Flores deputy regent Agustinus Payong Boli estimated that as many as 60 people in his municipality had died. “Many people died here because the village was hit by both landslides and flash floods,” he told reporters.
Injured people on the islands have been evacuated to neighbouring villages that were unaffected, and to local hospitals and other health centres.
Flash floods and fatal landslides are common across the Indonesian archipelago during the monsoon season, which usually runs from November to March.