Singapore PM Lee Hsien Loong has passed out as he was giving a speech during a National Day rally.
The live broadcast was suspended as physicians attended to him.
Mr Lee had been “unsteady because of prolonged standing, heat and dehydration,” a statement from his office said. “His heart is fine and he did not have a stroke.”
He afterwards resumed his speech to applause. Lee Hsien Loong, 64, has been in office since August 2004.
He had surgery to remove his prostate gland last year. He was diagnosed with lymphoma in the 1990s but recovered.
Mr Lee’s People’s Action Party (PAP) has been in power since 1959, when Singapore was still a self governing British colony.
A former army officer and Cambridge-educated mathematician, he followed his father Lee Kwan Yew into politics in 1984.
Mr Lee said a new prime minister “must be prepared” to take office after the following general election.
The PAP won a crucial victory in last year’s elections. Elections in Singapore are held every five years.
As prime minister, the younger Mr Lee has launched policies to establish a competitive market, investing in research and development, introducing new programmes to update the education system and transforming the city-state.