Several outlets, including the BBC, reported that the 52-year-old Portuguese had been dismissed by the club for the second time, having been sacked at the end of his previous spell in 2007.
A Chelsea spokesperson could not be reached for confirmation.
Mourinho led Chelsea to a Premier League and League Cup double last season, after returning to the club in 2013, but they are currently one point above the relegation zone after nine defeats in 16 games.
Juande Ramos, the former Tottenham Hotspur and Sevilla manager, and Dutchman Guus Hiddink have been cited as potential short-term replacements.
Pep Guardiola, the Bayern Munich coach, and Carlo Ancelotti, who managed Chelsea between 2009 and 2011, are reported to be possible long-term successors.
Mourinho is reported to have been informed of his fate in a meeting with club officials on Thursday afternoon.
In what looks to have been his final Chelsea game, his side were beaten 2-1 at Leicester City on Monday — a club managed by Claudio Ranieri, who he replaced at Stamford Bridge when he first arrived in England in 2004.
Mourinho was scathing in his assessment of his players’ display afterwards, saying: “I feel like my work was betrayed.”
With Chelsea having swept to the title by eight points last season, their recent collapse has baffled pundits.
As well as floundering in the league, they were knocked out of the League Cup on penalties by Stoke City, although they have reached the Champions League last 16, where they will face Paris Saint-Germain.