Singapore Prime Minister Lee Hsien Loong will be on medical leave until Aug. 29 on the advice of his doctors, his office said on Monday.

Lee took ill while delivering a National Day rally speech on Sunday but returned to the stage after a break of about an hour.

Lee's illness was brought on by a temporary drop in blood pressure due to prolonged standing, exhaustion and dehydration, the prime minister's office said in a statement.

Doctors had confirmed there were no cardiac abnormalities and no stroke, the office said.

Deputy Prime Minister Teo Chee Hean will cover the duties of the prime minister in his absence.