A telecoms blackout has reportedly hit Sumy Oblast in northeastern Ukraine, marking one of the most serious communications disruptions of the conflict so far.

The blackout was reported by the internet shutdown tracker NetBlocks on March 3rd at 8:23PM local time (1:23PM ET).

NetBlocks said that residents had reported massive blasts at a thermal power plant and electrical substation. A power outage tracker monitoring the region also said that it was no longer receiving data for Sumy Oblast.

Sumy Oblast is one of 24 administrative regions, known as “oblasts,” that make up Ukraine and has a population of roughly one million people.

Social media users reported that explosions had damaged the combined heat and power (CHP) plant in Sumy, resulting in a loss of heat, water and electricity. A video shared by a journalist from the Indian Deccan Herald newspaper reported to show Indian students sheltering from bombardment in the region and appeared to confirm details of the explosion and power cut. The city of Sumy has been a particular focus of media coverage in India after it emerged that an estimated 600-700 Indian students at Sumy State University were stranded and unable to leave.

The communications blackout in Sumy Oblast is the most serious outage since the Russian invasion began and appears to be on a larger scale than incidents reported in Kharkiv and Kyiv. On February 23rd, areas of Kharkiv and the surrounding region lost connectivity after infrastructure belonging to the internet service provider Triolan was damaged, although internet services were mostly restored shortly afterward.

While some analysts have expressed fears of a more widespread internet outage, it has so far failed to materialize. Some Ukrainians are now able to access satellite internet through SpaceX’s Starlink service after Ukraine’s vice prime minister tweeted to Elon Musk requesting that the service be extended to cover the country.