A local official told Reuters on Tuesday that two trains operating on single-track monorails collided at a hydroelectric project under construction in Uttarakhand, northern India, injuring at least 109 workers.

The official added that most injuries were minor, while four workers sustained fractures.

The collision occurred inside a tunnel in the town of Bheepalkoti, where the hydroelectric project is operated by Tehri Development Corporation, partly owned by NTPC.