Many southerners in Yemen feel that officials in the north have exploited their resources and cut them off from jobs and influence.
Thousands of people have taken to the streets of Aden demanding the secession of southern Yemen.
The mass gathering comes ten days after a group of regional politicians declared a separatist government led by former Aden governor Aidroos al Zubaidi.
The group calls for the return to the borders of 1990, before the country's unification.
Aidaroos al Zubaidi made his announcement in a televised address in front of the flag of the former nation of South Yemen, whose forces were defeated by the north in 1994 and brought into a reunified country.
The announcement raises the prospect of more division in an already complex conflict in the impoverished Arabian Peninsular country, where Saudi Arabia is leading a coalition of Gulf Arab forces against Houthi militants allied to Iran.
Meanwhile, the World Health Organisation says a cholera outbreak in Yemen is spreading at an alarming rate. The infection has killed 315 people so far.
More than half of the country's medical facilities are no longer functioning. Yemenis are suffering from a significant lack of food and clean water due to the ongoing war between the government and Houthi rebels.