Sudan's long-reigning president Omar al-Bashir has stepped down after being forced from his position by the military, according to senior officials.
A statement from the army is expected imminently to provide further detail of the situation.
The circumstances at present are vague and his location is also unclear.
This development comes after rumours of a coup to replace the president of 30 years intensified after mass street protests against his rule.
Two officials in high positions in the government and the military said the army was in talks about forming a transitional government.
Pan-Arab TV networks also carried unconfirmed reports Mr al-Bashir had stepped down and senior ruling party officials were being arrested.
Footage showed masses heading towards the presidential palace in the capital Khartoum, waving the national flag, chanting and clapping.
Armoured vehicles and tanks are parked in the streets and near bridges over the Nile River, according to reports.
They are also said to be in the vicinity of the military headquarters, where thousands were awaiting the army statement.
Crowds had been urged to converge and join a sit-in under way in Khartoum since the weekend.
Protest organisers issued a statement vowing to remain in the streets until the "regime steps down completely and power is handed to a civilian transitional government".
There were attempts to break up the sit-in, leaving 22 dead since Saturday.
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