The U.S. Geological Survey said webcam images showed lava flow within the Halemaʻumaʻu crater in the volcano's summit caldera.
The agency upgraded the volcano's alert level from watch to warning and said it was evaluating possible hazards. So far the eruption has been contained to the crater, it said.
The volcano, in Volcanoes National Park on Hawaii’s Big Island, has been erupting often since 1983.
In 2018, an eruption from fissures in its lower East Rift Zone covered 13 square miles with lava, destroying 700 homes and other buildings.
Most recently, Kilauea erupted between September 2021 and last month.
In November, another eruption on Hawaii's Big Island — from Mauna Loa, the world's largest active volcano — came after a series of large earthquakes. It was its first eruption in 38 years.
A month later, the USGS's Hawaiian Volcano Observatory said Mauna Loa's eruptions had ceased.