Thousands protested across Sudan against military rule on the anniversary Wednesday of previous popular uprisings, most recently against autocrat Omar al-Bashir three years ago.
Security forces fired tear gas at demonstrators in the capital Khartoum, its twin city of Omdurman, and in Wad Madani to the south, witnesses and AFP correspondents said.
They also "stormed Al-Jawda hospital and fired tear gas inside, scaring patients and health workers and causing suffocation among some of them", said the independent Central Committee of Sudan Doctors.
Sudan has grappled with an October 25 coup led by army chief Abdel Fattah al-Burhan that has derailed a political transition period and hammered the economy of one of the world's poorest countries.
Pro-democracy activists had warned online of a people power "earthquake of April 6" -- a momentous day in Sudan's history that was key in bringing down earlier strongmen.
In 1985, the day saw the ouster of president Jaafar Nimeiri following a popular uprising. In 2019 it marked the start of a mass sit-in outside army headquarters, after months of protests, against Bashir's three decades in power.
"It is an important day... so we expect many to take to the streets despite the heat and Ramadan," the Muslim month of fasting, said one Khartoum protester, Badwi Bashir.
"We just want to bring down the coup (leadership) and end the prospect of any future coups."
Sudan's latest putsch has "set fire to all aspects of life, turning our country into an arena of crises," said the civilian alliance Forces of Freedom and Change, or FFC.
Security forces had earlier sealed off key bridges and deployed around the presidential palace and army headquarters.
In Omdurman, protesters broke through barbed wire blockades and marched through streets leading to the parliament building, according to an AFP correspondent.
Protesters marched in the eastern state of Gedaref with banners that read "No to military rule" and "Away with the government of hunger", said one witness, Ahmed Salah.
Demonstrations were also held in several cities across the Darfur region, the central state of North Kordofan and the Red Sea city of Port Sudan, according to witnesses.
Five days after the start of the 2019 sit-in, generals bowed to the pressure on the streets to remove Bashir.
But the protesters stayed on to press for civilian rule, only to be dispersed in a crackdown in June that year by men in military fatigues that claimed 128 lives according to medics.
Sudan's civilian and military leaders later agreed on a transition of power, which promised greater international engagement for the country as well as foreign aid and investment.
But last October's coup upended those plans, leading to the current wave of protests. At least 93 people have been killed and hundreds wounded in the crackdown since, medics say.
"We have to defeat the coup," FFC spokesman Jaafar Hassan said last week.
"We have tried a partnership with the military, and it failed, ending in this coup, and we shouldn't do this again."
Burhan said last Saturday he would only "hand over power to an honest, elected authority, accepted by the all the Sudanese people".
The United States on Wednesday warned against "the use of any violence" and demanded Sudanese authorities "keep their word and hold accountable those responsible for abuses."
Since the coup, Sudan's already ailing economy has suffered severe blows, as Western donors cut crucial aid pending the restoration of a transition to civilian rule.
Prices of food, fuel and basic commodities have soared and crime has spiked. Violence has intensified in remote areas, particularly the restive Darfur region, the UN says.
Burhan last week threatened to expel UN special representative Volker Perthes, accusing him of "interference" in the country's affairs after Perthes warned of the deepening crisis in Sudan during a UN Security Council briefing.