The former pope is "absolutely lucid and alert" and his condition is serious but stable, the Vatican has said.
Vatican spokesman Matteo Bruni said: "The Pope Emeritus was able to rest well last night. He is absolutely lucid and alert today, although his condition remains serious, the situation at the moment is stable.
"Pope Francis renews his invitation to pray for him and accompany him in these difficult hours."
The current pope did not elaborate on Benedict's condition when he appealed for people to pray for him at the end of his general audience on Wednesday.
The Vatican said after the service that the 95-year-old's condition had suddenly "worsened due to age".
A spokesperson said he was receiving constant medical care and his condition was "under control".
Benedict became the first pope in some 600 years to resign in 2013, due to deteriorating" health, with the former pontiff taking the title pope emeritus.
He has been living in the Vatican and dedicating his life to prayer and meditation, but has become increasingly frail in recent years.
Some cardinals and lawyers have questioned Benedict's decisions on retirement, including his continued wearing of the white cassock of the papacy.
Another point of contention has been Benedict refusing to revert back to his birth name, Joseph Ratzinger.
Critics say those choices and his continued presence in the Vatican have been confusing for Catholics and threaten the unity of the Church.
They say traditionalists have been able to use Benedict as a conservative point of reference when they've been unhappy with Francis's decisions.