Union Minister for Parliamentary Affairs Ananth Kumar died on Monday at a private hospital here due to multiple organ failure, a BJP spokesman said. He was 59.
"Kumar passed away at around 3 a.m. at Shankara Cancer Hospital three weeks after he was admitted on return from the US on October 21," party's state unit spokesman S. Shantaram told IANS.
The Karnataka government declared a three-day mourning across the state and one-day public holiday for Monday as a mark of respect.
The departed leader was also the Chemicals and Fertilisers Minister in the NDA-led government since May 2014.
A six-time parliamentarian from the Bengaluru South Lok Sabha constituency since 1996, Ananth Kumar had been undergoing treatment for cancer in the UK and US since August.
"He first went to London after the monsoon session of Parliament in July-August and later shifted to a New York hospital.
"The cancer had spread to other parts of his body that resulted in his multi-organ failure and death," said Shantaram.
The late Union Minister is survived by his widow Tejaswani, two daughters Aishwaraya and Vijayeta, younger brother Nand Kumar and younger sister Suhasini.
Kumar's body was shifted to his residence and home-office at Basavangudi here.
"It will be kept in state at the National College grounds in Basavangudi for the public to pay homage till the last rites on Tuesday," said the party official.
"The national flag will fly half-mast on public buildings across the state and all official engagements are cancelled till Wednesday," the Congress-JD-S government here announced.
State and central government offices will remain closed on Monday as a tribute to Kumar, a state official told IANS.
The Karnataka Education Department declared holiday for all schools and colleges in the city on Monday as a mark of respect.
As news of Kumar's demise spread across the city, hundreds of people, including party's state unit leaders rushed to his residence to pay their last respects.
Several Bharatiya Janata Party's leaders, including state unit chief B.S. Yeddyurappa and legislators R. Ashok and Suresh Kumar visited Kumar's house and condoled his untimely death.
"Prime Minister Narendra Modi, Union Ministers and the party's national leadership are expected to attend Kumar's state funeral in the city on Tuesday," Shantaram said.
President Ram Nath Kovind, Narendra Modi, Rajnath Singh, D.V. Sadananda Gowda, Arun Jaitely, Nirmala Sitharaman and Nitin Gadkari mourned Kumar's death and expressed condolence to the bereaved family.
Karnataka Chief Minister H.D. Kumaraswamy, Deputy Chief Minister G. Parameshwara, cabinet ministers of the Janata Dal-Secular (JD-S) and Congress coalition government joined BJP's state unit leaders and cadres in condoling Ananth Kumar's death.