A file photo shows the southwest coast of Tonga's main island Tongatapu in November 2006. Photo: AAP
Authorities in Tonga are monitoring activity around an underwater vent which is creating a plume of steam over 3000 metres high.
The Deputy Secretary of Natural Resources and Geologist Taniela Kula says the vent is about 55 kilometres northwest of Tonga's main island Tongatapu.
Mr Kula says contrary to some reports, the steam is not coming from the underwater volcano Hunga Ha'apai which erupted in 2009 but a vent to the southwest.
He says while the steam cloud is impressive it's not disrupting air traffic at this stage.
"We can see from Nuku'alofa where the steam is going up from the horizon so it's pretty active but there's no sign of ash coming out of the vent. It's water vapour but no detection of ash. The steam is still growing and we are expecting some more eruptions coming up but mostly steam."