HOUSTON - Fire broke out at a nuclear power plant Tuesday in the US state of Texas, forcing one of two units to be shut down, US media reported.

No injuries were reported in the fire, which erupted in the Unit 2 main transformer of the South Texas Project Electric Generating Station near Bay City, according to ABC news.

Officials said the fire was quickly brought under control and extinguished. The unit was automatically taken offline, but the company's other transformer, Unit 1, remained operating at 100 percent power.

The fire prompted company officials to declare an "unusual event", its lowest level emergency classification, according to the report.

A spokesperson said the classification indicates a minor problem at the facility but poses no hazard to the public or to plant workers.

The plant is about 140 km southwest of Houston. The two 1,350-megawatt generators, owned by NRG Energy, CPS Energy and Austin Energy, serve 2 million users.