Das, who was seated next to JD(U) president Sharad Yadav, was taken ill while Agriculture Minister Narendra Singh was speaking at the JD(U)'s 'Chintan Shivir' on the second and concluding day, JD(U) sources said.
Noticing Das's health condition, Chief Minister Nitish Kumar rose from his seat and called for an ambulance to take the ailing leader to hospital for treatment, sources said.
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He was offered sweets by the party workers before being bodily lifted by them to an ambulance on way to a hospital under the Chief Minister's supervision.
The JD(U) delegates prayed for the well being of the party MP.
The JD(U) convention remained suspended for about 15 minutes in the wake of the deterioration of the JD(U) MP's health.
Das, aged about 100 years, is the Lok Sabha MP from Hajipur and also the Deputy Leader of the JD(U) in the Lok Sabha.
He had defeated the LJP supremo Ramvilas Paswan in the 2009 general elections.