SHILLONG, India -- Avul Pakir Jainulabdeen Abdul Kalama, a rocket scientist who became one of India's most popular presidents, died Monday in the far eastern city of Shillong, the prime minister said. He was 83.

Kalama died of a cardiac arrest; he had collapsed during a lecture and was declared dead upon arrival at the hospital, The Washington Post reported.

Indian Prime Minister Narendra Modi announced Kalama's death on Twitter.

"India mourns the loss of a great scientist, a wonderful president and above all an inspiring individual," he wrote.

Narendra said he "marveled" at Kalama's intellect and admired the former president for his dedication to his students and young people.

"He loved students and spent his final moments among them," Narendra said.

'Kalam had won hearts with warmth, wisdom' said Congress Vice-President Rahul Gandhi

Kalam was instrumental in 1998 nuclear tests that led to international sanctions against India. He assisted in developing India's missile technology and won the highest civilian award in the country for his role.

He served as president from 2002 to 2007. During his term, he often took the unprecedented step of inviting members of the public -- of a variety of castes -- into the presidential palace.

"India has today lost one of its most inspirational persons. Dr. Kalam was not merely the president but he was to every Indian a role model and an ideal citizen," said Finance Minister Arun Jaitley. "Everything about him was positive. He thought well, he had positive ideas. His contribution as a scientist, his contribution as a president was unparalleled. He has left a void for all of us."Danielle Haynes> BNN