Japan's Meteorological Agency has modified its view of the eruption at Sakurajima in Kagoshima Prefecture, southwestern Japan, on Sunday morning. It now says that what appeared to be pyroclastic flows -- a dense current of hot gas and volcanic matter -- were actually volcanic fumes.

After the eruption, the agency initially said it confirmed that a mixture of lava, volcanic ash and gas had flowed for a distance of 1.8 kilometers from the crater.

Officials therefore expanded the alert zone from the crater to 2.4 kilometers from 2 kilometers, covering areas close to a residential district.

But they later said that an on-site inspection did not find any high-temperature areas supposed to exist after pyroclastic flows. There were also no traces of trees that had been knocked down.

The agency concluded that what it first thought to be pyroclastic flows were in fact volcanic fumes that had drifted down the slope. It returned the alert zone to the pre-eruption size.