"We were having our weekly Cabinet meeting just now when Heng Swee Keat suddenly collapsed," Lee wrote on his Facebook page.
"The doctors in Cabinet (we have three) attended to him immediately. We called an ambulance, which took him to TTSH," he said, referring to the state-run Tan Tock Seng Hospital.
"A CT scan showed that he had had a stroke. Hope Swee Keat will be alright -- he is a valuable member of my team."
Prior to entering politics, he was the Managing Director of the Monetary Authority of Singapore, the de facto central bank.
Deputy Prime Minister Teo Chee Hean and other ministers took to Facebook wishing him early recovery. "Praying for the recovery of our colleague Swee Keat," he wrote.
Deputy Tharman Shanmugaratnam wrote: "Let's hope and pray for Heng Swee Keat.
