Indonesian authorities on Tuesday asked people to avoid the coast in places affected by a tsunami last week that has claimed at least 429 lives, AP reported. The tsunami struck the areas around the Sunda Strait without warning after a portion of the volcanic Anak Krakatoa island fell into the ocean.

The country’s Meteorology, Geophysics and Climatology Agency advised citizens to stay at least 500 m and up to 1 km away from the coastline along the Sunda Strait, which separates Indonesia’s two main islands of Java and Sumatra. The advisory was issued on the 14th anniversary of the Indian Ocean earthquake and tsunami that struck Banda Aceh in 2004.

Agency head Dwikorita Karnawati said high waves and heavy rainfall were possible on Wednesday and government workers were closely monitoring Anak Krakatoa’s eruptions.

“All these conditions could potentially cause landslides at the cliffs of the crater into the sea, and we fear that that could trigger a tsunami,” Karnawati said, urging communities to remain cautious but not panic.

Residents of coastal areas in the area evacuated their houses after a fresh volcanic eruption on Tuesday, The Straits Times reported. Karnawati warned that the current “extreme weather and high tides”, coupled with Anak Krakatoa’s continued tremors, could trigger another tsunami.

Meanwhile, torrential rainfall on Wednesday hampered rescue efforts and delayed the delivery of assistance to isolated villages and evacuation shelters. The disaster agency said hundreds of residents, who remain stranded on islands in the Sunda Strait, will be airlifted or taken by boat to shelters.

The agency said it has also dispatched helicopters to airdrop supplies into a few villages located along the coastlines of western Java and south Sumatra.