"This is a young man who sells cigarettes because of unemployment," shouted the man before immolating himself on Habib Bourguiba avenue in front of the municipal building, according to a witness.
"Allahu Akbar! (God is greatest!)" said the badly burned man who was still conscious as he was rushed to the Ben Arous hospital in a Tunis suburb by emergency services, the witness said.
Passers-by rushed to douse the flames but not before the man, believed to be in his 20s, had suffered serious burn wounds.
A hospital source said he was "in a critical condition and only his feet were not burned."
"We will give him an anaesthetic because he is feeling the," the source said, adding that the unidentified man had said to a doctor: "I am sick and nobody wants to take care of me."
Habib Bourguiba avenue in central Tunis is the Mecca of the 2011 revolution that ousted former dictator Zine El Abidine Ben Ali. On the avenue's sidewalks many Tunisians eke out a living by selling cigarettes.
The number of people committing suicide or attempting to take their own lives has multiplied in Tunisia since a young street vendor set himself on fire on December 17, 2010, in a drastic act of protest against police harassment.
Mohamed Bouazizi's death in the town of Sidi Bouzid ignited a mass uprising that toppled ex-dictator Zine El Abidine Ben Ali the following month and touched off the Arab Spring uprisings.
Economic and social difficulties were the key factors that brought down Ben Ali's regime and two years since his ouster unemployment and poverty continue to plague the north African country.
The simmering discontent has in the past few months sparked strikes and protests which often degenerate into violence. In November around 300 people were wounded in a week of clashes with police in the northwest of the country.
Tunisia has also been struggling to emerge from a political crisis exacerbated by the daylight murder on February 6 murder of Chokri Belaid, a leftist opposition leader.
Later Tuesday, premier-designate Ali Larayedh was to seek a vote of confidence on his new cabinet line-up from lawmakers in the National Constituent Assembly.
