A paramilitary officer charged with guarding a nuclear plant shot and killed three of his colleagues on Wednesday in a shooting spree at their base in southern India, authorities said.

It was not immediately clear what provoked the attack, which took place early Wednesday morning at a Central Industrial Security Force (CISF) base in southern Tamil Nadu state, around 10 kilometres (six miles) away from the Kalpakkam power plant.

The CISF is tasked with guarding key government offices and monuments such as the Taj Mahal, as well as nuclear plants.

"They had assembled for morning duty when he opened fire," CISF spokesman Hemendra Singh told AFP.

"We are looking into the matter and checking what triggered this. But we immediately detained him and handed him over to the police."

He said the officer, Vijay Pratap Singh, was highly experienced and "in shock" after the attack.

"It is not as if he is a new fellow, he has been doing this service for 24 years. After questioning there will be more clarity on why it happened," he added.

Operations at the nuclear power plant were unaffected, Singh said.

The Kalpakkam nuclear power facility was battered by a massive tsunami in the Indian Ocean in 2004 that left 6,170 people dead in India.

Water seeped into the facility that is located on the coast after the tsunami hit. It resumed operations a year later.

India hopes to build many such plants as part of its ambitious plan to generate 63,000 megawatts of nuclear power by 2030 -- a near 15-fold rise from current levels, according to the Nuclear Power Corp.