Indonesian authorities on Sunday maintained a red alert at smouldering Mount Merapi, as activity at the volcano continued to intensify for an eighth straight day since an earthquake rocked the region.

In the first six hours of Sunday the volcano spewed 118 lava trails and six heat clouds, said Subandriyo, head of the Merapi section at the vulcanology office in Yogyakarta, the main city in the quake zone.

On Saturday, Merapi belched out nearly 500 red-hot lava flows, plumes of smoke stretching 800 meters (2,500 feet) into the sky and more than 100 heat clouds, some of them drifting four kilometers (2.5 miles) down the peak.

Ratdomo Purbo, who heads the vulcanology office in Yogyakarta, was quoted by the Republika newspaper as saying the magma dome atop Merapi had almost doubled in volume to some four million cubic meters, nearly covering the entire crater.

"Because there is no more space to accommodate (the dome's growth), the amount of magma emitted from within the mountain will immediately fall," Purbo said, explaining the increased number of lava trails and heat clouds.

But Surono, a vulcanologist at the government's geological disaster management center, said a major eruption was unlikely.

"Every day, magma is coming out from the body of the volcano and it is adding to the dome, which is becoming bigger. So the pressure and the energy in the volcano is decreasing automatically," he told AFP in Yogyakarta.

"So there is not enough energy for a big explosion."