KHARTOUM (Reuters) - Thousands of protesters held a sit-in outside Sudanese President Omar al-Bashir’s residence in central Khartoum on Sunday, and crowds chanting anti-government slogans filled several main streets, witnesses said.

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Sudan has seen sustained protests against Bashir and his National Congress Party since Dec. 19. Security forces have fired tear gas, stun grenades and live bullets to disperse protesters and dozens have been killed during demonstrations.

Bashir has refused to step down, saying that his opponents need to seek power through the ballot box.

On Sunday evening, dozens of demonstrations took place in the Sudanese capital, eyewitnesses said. Protesters marched in several streets of central Khartoum, setting fire to car tyres and blocking a main road, a Reuters witness said. Demonstrators also blocked a bridge that connects Khartoum and Khartoum North. No police officers or other security forces personnel could be seen, eyewitnesses said.

Sudan earlier suffered a total power blackout, the ministry of water resources, irrigation and electricity said without explaining the cause of the outage. Electricity was later restored in some areas.

Since the sit-in began outside of the presidential residence on Saturday, security forces had fired tear gas several times in an attempt to clear the protesters, but thousands remained on Sunday.

Apparently emboldened by the success of similar but much larger protests in Algeria, which forced ailing President Abdelaziz Bouteflika to step down last week, Sudanese activists called for Saturday’s protests. The demonstrations marked the anniversary of the 1985 military coup that overthrew autocratic President Jaafar Nimeiri after mass protests against his rule.

The protesters urged the military to side with them once more in their bid to push Bashir out of power.

The compound which houses the presidential residence is the most heavily guarded in Sudan. It is also home to the defense ministry and the headquarters of the powerful National Intelligence and Security Service.

On Saturday at least one person died during protests in Omdurman, across the Nile from Khartoum, state news agency SUNA said without providing detail on the cause of death.

The person killed was a laboratory doctor who succumbed to his injuries, according to a statement from an opposition doctors’ committee. Medical staff have played a prominent role in the protests.

SUNA said other civilians and police officers were wounded on Saturday in Omdurman, the scene of protests late into the evening that subsided by Sunday morning.

The sit-in outside the compound appeared to mirror 2011 Arab Spring protests, in which demonstrators in Cairo and other Arab capitals camped out in public squares for days to demand a change in rule.

Police and security forces on Saturday blocked all bridges leading to the capital’s center from Khartoum North and Omdurman, across the River Nile to the north and west respectively, in what appeared to be a bid to prevent the sit-in from swelling.

They remained closed on Sunday, causing major traffic jams. Hundreds of people were crossing into Khartoum from Omdurman via Victory Bridge by foot on Sunday morning, a Reuters witness said, as cars stood at a standstill for hours.