At least 18 elephants are suspected to have been killed by lightning in northeastern India, officials said as they launched an inquiry into the incident.

Forest officials and a local lawmaker, Jitu Goswami, said they believed the animals died after lightning struck a forest in Nagaon district in central Assam during a storm on Wednesday.

Assam's Chief Minister said in a statement that he was concerned about the deaths of such a "huge number of elephants".

"Deeply pained by the death of 18 elephants last night due to massive thunderstorm under Kothiatoli Range in Nagaon," Assam's Forest Minister Parimal Suklabaidya tweeted, adding that he would visit the forest with wildlife officials today.

Four elephant carcasses were recovered yesterday, forest officials said.

India is home to nearly 30,000 elephants, around 60% of the wild Asian elephant population.

Assam's Chief Minister said he was concerned about the deaths of such a 'huge number of elephants'