Indonesian rescue teams on Wednesday struggled to reach remote areas on the western coast of Java amid an “extreme weather” rain warning after a tsunami killed more than 400 people last week.

Heavy rain lashed fishing villages along the coast, muddying roads and holding up convoys delivering heavy machinery and aid to isolated areas while authorities urged residents to stay away from the shore in case of further waves.

Clouds of ash spewed from the nearby Anak Krakatau, almost obscuring the volcanic island where a crater collapse at high tide on Saturday sent waves up to 16ft high smashing into the coast on the Sunda Strait, between Java and Sumatra islands.

Indonesia’s meteorology agency (BMKG) said the rough weather could make the volcano’s crater more fragile.

“We have developed a monitoring system focused specifically on the volcanic tremors at Anak Krakatau so that we can issue early warnings,” said BMKG head Dwikorita Karnawati, adding that a 2km exclusion zone had been imposed.

The confirmed death toll is 430, with at least 159 people missing. A state of emergency has been declared until January 4, which authorities hope will make it easier to deploy assistance, said Sutopo Purwo Nugroho, spokesperson for the national disaster mitigation agency.

Search and rescue teams were focused on the town of Sumur near the southwest tip of Java, but “the roads are damaged and clogged” and helicopters had to be deployed to carry out assessments and evacuations, he added.

Along the coast, thousands of people are staying in tents and temporary shelters like mosques or schools. Rice and instant noodles have been delivered to many shelters, but clean water, wet weather gear, fresh clothes, and blankets are in short supply, some evacuees said.

Ade Hasanah, 45, staying in an emergency centre with her children, said people were being told not to return to their homes.