WHAKATANE, New Zealand — Rescue workers on Wednesday were again forced to delay attempts to reach White Island to recover the bodies of people believed to have been killed in a volcanic eruption there. The authorities said conditions were still too dangerous and unpredictable to risk the attempt.

A volcanologist, Graham Leonard, said at a news conference that the chance of another eruption on the scale of Monday’s explosion happening within the next 24 hours was between 40 and 60 percent. He added that for anyone traveling to the volcanic island now, even walking and breathing would be a challenge.

Dozens of people were rescued after the eruption Monday, but the authorities later said that eight people were still believed to be on the island and presumed dead. On Wednesday, the New Zealand police released a list of nine people who they said were officially considered missing, seven from Australia and two from New Zealand. The police would not explain the discrepancy.

Deputy Commissioner John Tims of the New Zealand police expressed frustration that recovery efforts had been delayed for a second day, but said the risks — including the hazards that toxic fumes could pose to rescue crews — outweighed the sense of urgency.