"Heard that you're not feeling well. I hope you're all right. Get well soon," Prime Minister Najib Abdul Razak said in a Twitter message to Singapore Prime Minister Lee Hsien Loong last last night.

"Thanks for your good wishes. My doctors tell me I should be OK," Lee replied around 2am.

Lee was taken ill while speaking at the country's National Day Rally around 9.40pm yesterday.

Lee, 64, was scheduled to end his English speech at 10pm after delivering his Malay and Mandarin versions at 6.45pm.

Lee managed to continue his speech after almost an hour of rest and wrapped up his speech in 15 minutes.

Immediately after delivering his speech, Lee went to the Singapore General Hospital for a precautionary check-up.

In his National Day speech, Lee had touched on Singapore's relationship with Malaysia and Indonesia.

He described both countries as Singapore's two most important partners.

Last month, Lee said he was in Putrajaya, Malaysia, to witness the signing of the Memorandum of Understanding on the High Speed Rail between Singapore and Malaysia.

"PM Najib hosted us to lunch. The durian was good, but the High Speed Rail will be better!" he said while the large screen behind him showed a photo of him with Najib.

- Bernama