The `Baby` singer was diagnosed with a bad chest infection ahead of his show in capital city Manila but refused to cancel or cut his performance short, leading to him being sick backstage between songs.
A source told website Perezhilton.com: "Justin was advised to either cancel the show or do an abbreviated set, but he insisted on going on. So they cut down the show, but once the show started he kept going."
The 17-year-old pop sensation had been greeted by hundreds of screaming fans outside the city`s SM Mall of Asia, and despite his illness he enjoyed the show.
He wrote on his twitter page afterwards: "The streets of Manila are filled - this is crazy. great energy. Sick or not, that show went hard! That show was great but tough. real sick. time to rest. (sic)"
Justin later thanked fans for coming to see him, tweeting: "Thank You for always supporting me and helping me live my dream.
"Thank You for being the most loyal amazing fans in the world. Even when im sick feels good to come on here and see the love. gonna rest up and hope to get better. ITHANKYOU (sic)."
Justin has two days off before his next concert, and left the Philippines for Hong Kong at 10am local time on 11.05.11.
Despite still being sick, he signed autographs for fans at the exit of presidential lounge at the airport arrival area and was the last to board his flight, which was almost delayed after passengers and airline personnel mobbed him to get his signature and photos.