Hungary has sunk two barges in the Danube in an emergency effort to keep the Paks nuclear power plant operating amid record-low water levels.

The plant is currently running at around 25% of its capacity and relies on the river for cooling.

Crews deliberately submerged two 80-meter barges near the plant, while military helicopters dropped concrete blocks weighing up to two tonnes into the river and trucks dumped rocks to build an underwater embankment.

The sunken barges and concrete blocks are designed to slow the river's flow and raise water levels upstream by several centimeters, helping keep two turbines operating while a larger riverbed sill is constructed.

The emergency operation comes as Hungary faces a historic drought and extreme heat, putting increasing pressure on its energy system.

Neighboring Romania shut down its last operating reactor on Thursday because of low Danube water levels.

The crisis is also raising concerns over how nuclear power plants can adapt to increasingly severe droughts and heat linked to a changing climate.