BNP Secretary General Mirza Fakhrul Islam Alamgir was admitted to a hospital in Dhaka on Saturday morning (2 March) after suddenly falling ill.
He is currently receiving treatment at United Hospital in the capital's Gulshan, according to media reports.
Shairul Kabir Khan, a member of the BNP Media Cell, confirmed the development to reporters on Sunday (3 March).
Media sources indicate that Fakhrul had been feeling unwell for the past two days and was hospitalised following his doctor's recommendation.