Land formed by lava flowing from Mount Kilauea first appeared offshore last Thursday, off the northern edge of the Big Island, according to the United States Geological Survey (USGS).
It was noted by the Hawaii Volcano Observatory on Friday, as they took a morning flight over the island.
The new island is only a few metres offshore, and is thought to be between six and nine metres in diameter.
It is part of the lava flow running underwater away from the coastline.
The USGS thinks natural underwater pressures pushed the lava flow to the surface where it hardened. This process is very common and known as a tumulus.
If the lava keeps flowing, the new island could connect to the existing coastline.
However, if it begins to slow, it will most likely be eroded away by movements of the waves.
Residents of the Big Island will get the opportunity to name the new island.
USGS have said regardless of whether the island stays or disappears, naming it will be the responsibility of the local community.
Kilauea started erupting in May, sending a flow of lava into residential areas and eventually into the Pacific Ocean.
Despite destroying hundreds of homes, the eruption had been relatively safe from a public perspective.
However, an incident on Monday marked the most significant injury since the first explosion on May 3.
A total of 23 people were injured when a so-called lava bomb hit a tourist boat on Monday morning.
The lava punctured the boat’s roof and it was forced to return to harbour.
13 passengers were treated at the hospital, and another 10 passengers with superficial injuries were treated on arrival at the harbour.
One woman in her 20s was in serious condition with a fractured femur.
It was unclear exactly where or when the incident occurred. But from where lava is hitting the ocean to the harbour is about an hour’s boat ride, depending on waves.