Army tanks rolled onto the streets of Khartoum and the fate of President Omar al-Bashir was uncertain with military and government sources saying that the embattled leader had been relieved of his duties.
The Sudanese army is expected to make "an important announcement", state media said on Thursday, after months of protests against Bashir.
"The Sudanese army will issue an important statement soon. Wait for it," a television anchor said, without giving further details.
Thousands of people poured onto the streets of the capital as they waited hours for the announcement.
At least two army tanks, one with jubilant demonstrators on top, moved through the capital.
Witnesses reported gunfire near the military headquarters that have been at the centre of six days of a defiant sit-in.
The military's headquarters also houses Bashir's official residence and the defence ministry.
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The unrest erupted in December when demonstrations broke out over a rise in bread prices. They have grown to become the biggest challenge yet to Bashir's 30-year rule.
Crowds of demonstrators have spent five nights thronging the sprawling complex, singing and dancing to revolutionary songs.
Al Jazeera's Hiba Morgan, reporting from the Sudanese capital, Khartoum said there was a heavy security presence on the city's main roads.
"There are a lot of military trucks around the capital and around the main streets of the city. Most roads have been blocked especially those leading to the army HQ. There are a few roads opened for the protesters who have been participating in the sit-in," Morgan said.
"People are extremely happy even before the army made any announcement. People are celebrating and pouring into the sit-in area. Protesters are saying they are very confident that Bashir will resign," Morgan added.
The group spearheading the nationwide demonstrations urged residents of the capital to mass outside army headquarters.
"We call on our people from across the Khartoum capital and the region around to immediately go to the sit-in area and not leave from there until our next statement is issued," the Sudanese Professionals Association said.
The group also said they will not accept a military government to succeed President Bashir.