The world's highest concentration of invisible and toxic gas is currently over the Pacific following the Hunga Tonga-Hunga Haʻapai eruption in Tonga.
Due to the eruption in Tonga, Niwa says the world's highest concentration of sulphur dioxide (SO2) is currently over the Pacific. Now, the Fijian government are warning the Pacific nation could experience acidic rainfall.
"As previously advised, the Department of Environment is requesting that members of the public cover all household water tanks and stay indoors in the event of rain due to the risk of acid rain," a government spokesperson said.
In terms of New Zealand, SO2 has been wrapped into Cyclone Cody, east of the country.
Early indications from Niwa do not show extreme levels of SO2 in the stratosphere, however, it's still early and more measurements are being taken.
SO2 is an invisible pollutant that is toxic and is converted to sulphuric acid droplets over time.
"These aerosols can have a long-lasting radiative effect around the globe, reflecting incoming sunlight and lowering temperatures."
Meanwhile, in Tonga, Niwa says possible short-term hazards to human health include acid rain and "volcanic smog".
"While large & locally devastating for Tonga, the eruption looks unlikely to change the direction of the global temperature trend."
At 2.45pm, the National Emergency Management Agency (Nema) said strong and unusual currents are expected to continue until the volcanic activity in Tonga ends.
"Take care if you are in or near the water close to the shore," a spokesperson said.
A Royal NZ Air Force Orion aircraft left for Tonga early this morning and is due to send back images and video footage of the damage.
Crew members will assess the situation and determine exactly what help is needed, initially.
The situation has been hampered by the fact that communications networks in the island nation have been cut for close to 40 hours since the eruption and Tongans from around the world have struggled to make contact with loved ones back home.
Earlier today, Prime Minister Jacinda Ardern, joined by Minister of Defence Peeni Henare, told media that the arrival of a Royal NZ Air Force Orion in Tonga is now imminent.
She also acknowledged that supplies are ready to go - no matter what the status of the main airport in Tonga is.
On the Tonga Hunga Tonga-Hunga Haʻapai eruption, Ardern said an Air Force Lockheed C-130 would be dispatched. Another aircraft, a P-3K2 Orion, was already monitoring the situation.
Henare said it was important to ensure any vessels or craft deployed would need to have contact with authorities in Tonga.
Ardern said they have been communicating with people using satellite phones and information from people on the ground through other avenues - including via church ministers and familial links.
"We are getting back critical information that's helping with the planning."
The stand-up comes as the Government waits to get word on the extent of the damage caused by a giant volcano eruption late on Saturday afternoon, which resulted in tsunami waves wiping out homes on the coast and sending locals to higher ground.