PRIME Minister Lee Hsien Loong was "feeling unsteady because of prolonged standing, heat and dehydration" a Tweet from his Twitter account said on Sunday night.

"His heart is fine and he did not have a stroke," the Tweet added.

This update comes after Mr Lee took ill while speaking at the National Day Rally on Sunday. This happened around 9.15pm, during the English portion of Mr Lee's speech.

The rally was suspended shortly after. It is expected to resume shortly.