In the middle of the closing ceremony, 79-year-old Hu was led out of the hall by two men.
NRK's Asia correspondent Philip Lote is in Beijing.
He says videos on social media show Hu Jintao resisting being led away by guards.
- The way he left the meeting today is not made any less special by the fact that President Xi had to help Hu, who is clearly physically weakened, to sit down during the opening of the congress, he says.
It is speculated that health reasons may be behind the incident, Hu Jintao is said to have been seriously ill this summer.
But no official explanation for the incident has yet come.
- There are remarkable television images that lead to speculation.
I cannot say today what it might be due to, but it is clear that there is symbolism in the fact that Xi Jinping's representative as general secretary was apparently led away at the same time as his power was cemented, says Björn Jerdén, program manager for the Foreign Policy Institute's China Center, to TT.
When the American news channel CNN began to pay attention to the event, their signal in China was shut down by the censors, the channel states.
- As a "party elder", Hu Jintao still has great power, but unlike Xi Jinping, he represents a collective leadership, says Tilde Levin, SVT's incoming correspondent in China.