Black smoke has been seen from the chimney of the Sistine Chapel, meaning a new pope has not yet been elected, the BBC reports.
The cardinals gathered in the Vatican will therefore continue the process to elect a new head of the Catholic Church tomorrow.
Before the chapel doors shut earlier, the cardinals took an oath in which they promised to keep secret all matters related to the vote.
They are allowed no communication with the outside world until a new pope is elected.
Tomorrow morning, cardinals will have breakfast from around 06:30 (05:30 BST) ahead of Mass, before more votes scheduled for later in the day.
During the conclave, the cardinals live in the Casa Santa Marta, a five-storey guesthouse with 106 suites, 22 single rooms and a state apartment.
The conclave – the assembly of cardinals for the election of the pope – happens at the Sistine Chapel. Cardinals are forbidden from speaking to outsiders during this period.
While their seclusion could last for an indefinite period, both Pope Francis and his predecessor, Pope Benedict XVI, were elected after two days.
