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Bad weather and a massive ash column hampered efforts to assess whether Indonesia's Anak Krakatau volcano island could trigger another deadly tsunami as authorities said Friday the search for victims in the worst-affected province will continue into January.

Indonesia's disaster agency said that 426 people died in the Sunda Strait tsunami that struck Sumatra and Java without warning on Saturday. That was slightly lower than previously announced due to some victims being recorded twice. It said 23 are missing and more than 40,000 displaced.

High seas, clouds and constant eruptions have hindered attempts to visually inspect Anak Krakatau, the offspring of the infamous Krakatau volcano whose eruption in 1883 caused a period of global cooling. A large part of the volcano collapsed following an eruption Saturday, triggering the tsunami.

Authorities have warned Sunda Strait residents to stay a kilometer away from the coastline, citing the potential for another tsunami.

Gegar Prasetya, co-founder of the Tsunami Research Center Indonesia, said the severity of another potential tsunami could be less since satellite radar shows the volcano is now much smaller.

Saturday's tsunami hit more than 300 kilometers (186 miles) of coastline with waves of 2 meters (about 6 1/2 feet) or higher.

"According to the theory and my past research, the severity of the potential tsunami is reduced significantly. This morning we tried to take an aerial photo from the plane to confirm the satellite image but failed due to cloud cover," Prasetya said.

The disaster agency said the emergency period for Banten province in Java ends Jan. 9 and on Friday for Lampung province in Sumatra.

About 1,600 people have been evacuated from Sebesi island nearest Anak Krakatau and the remaining residents from its population of more than 2,800 will be transported Friday, the agency said.

Sulphur and thick ash from the continually erupting volcano has blanketed the island.

Indonesia on Thursday raised the danger level for the island volcano and more than doubled its no-go zone to 5 kilometers (3 miles).

Janine Krippner, a New Zealand-born volcanologist at Concord University in West Virginia, said it's hard to assess the risk of another Anak Krakatau collapse and tsunami because authorities don't know how stable its remaining edifice is.

"Ideally there would be an assessment of the volcano but it has been constantly erupting, preventing anyone getting close," she said.