Increasing tremors on a volcanic island in New Zealand on Wednesday prevented the recovery of the bodies of eight people thought to be left on the island, two days after an eruption engulfed dozens of tourists in steam and hot ash.

Six people were killed in Monday's explosion at White Island, which lies some 50 km (30 miles) off the mainland, with another eight missing and presumed dead and 30 injured.

Authorities monitoring the uninhabited island said conditions were worsening and there was now a 40 to 60 percent chance of a massive eruption similar to Monday in the next 24 hours.