Earthquake off Bali
© USGS
A 5.7 magnitude earthquake has hit Indonesia, northwest of Bali, as alert levels rise about the possibility of a volcanic explosion on the island.

A STRONG undersea earthquake has struck off the coast of holiday hotspot, Bali.

The 5.7 magnitude quake was detected northeast of Kemeduran, which is northwest of Bali, on Thursday, the US Geological Survey has confirmed. With a magnitude of almost 6, the earthquake is classified as moderate to strong. It was measured at a depth of 588km.

The news comes after tourists in Bali were warned to avoid the area around Mount Agung in the island's north amid fears it could erupt.

Indonesian officials have more than doubled the size of the no-go zone around the Mount Agung volcano and raised its alert level for the second time in less than a week, the Associated Press reported.

The volcano, about 72 kilometres from Kuta, is a popular tourist destination and hiking spot.

Indonesia's National Disaster Mitigation Agency said residents and tourists should stay six kilometres from the crater and up to 7.5 kilometres away to the north, southeast and wouthwest.

Locals living near Mount Agung volcano have also been seen evacuating their homes and groups of people were also seen gathering at a lookout point to watch Mount Agung for eruption.