TUNIS, Tunisia — On a day of unprecedented anger, in which tens of thousands of Egyptians took to their streets demanding an end to three decades of authoritarian rule, one voice stood out in the crowd.

“Tear gas. We r trapped inside a building. Help we r suffocating,” said Mohamed Abdelfattah in several postings on the social networking site Twitter. “Help !!! Arrested. Ikve been beaten a lot.”

Abdelfattah, a video journalist based in Alexandria, had gone to work Tuesday to cover the protests.

The civil unrest that has gripped Tunisia for more than a month has spread to Egypt, its relatively stable neighbor that has been led by President Hosni Mubarak for 29 years.

Security forces tried to quell the rare public outburst by Egyptians calling for political and economic reforms after calls for a second day of demonstrations on Wednesday.

On Tuesday, as many as 15,000 people chanted for freedom from oppression on the streets of Cairo, including outside parliament, the ruling party's headquarters, and in Tahrir Square, the bustling city center home to the famous Egyptian Museum and several five-star hotels. Clashes erupted after protesters tossed rocks at police and burst through a cordon of riot soldiers, who responded with beatings and tear gas, on Tuesday.

Security vehicles also doused protesters with high-pressure water cannons.

In one of the most dramatic videos captured at Tuesday’s scene, a defiant Egyptian youth stood up to a water-cannon truck in the middle of a Cairo street, eventually wrestling control of the hose.

Two protesters were killed and more than 60 others injured by exposure to tear gas during protests in the city of Suez, according to the Reuters news agency. One security official was also reportedly killed in clashes.

More than 70 demonstrators were arrested on Tuesday, according to local news reports.

Small-scale political and economic protests have been very common in Egypt over the past few years.

But Tuesday’s demonstrations defied most expectations — even, apparently, the country’s vast security forces, which appeared largely outnumbered and overrun in several cities.

The protests were loosely organized through the social networking site Facebook, on a page devoted to Khaled Said, a young man allegedly tortured and killed by police in Alexandria last summer.

The eruption of widespread anger on the streets of Egypt, however, has much deeper roots.

In his three decades of rule, Mubarak has watched as rising inflation and growing unemployment added to an already stagnating economy.

Neo-liberal economic reforms in the past decade were widely criticized, having served the country’s rich, without trickling down to average citizens.

Around a fifth of Egypt’s nearly 80 million residents live on or below the poverty line.

If college graduates in Egypt are able to find work, they can expect to make the national minimum wage, roughly $70 a month.

And for opposing voices, change doesn’t come easy.

Political competition in Egypt is virtually non-existent. Elections frequently take place amid allegations of vote-rigging and intimidation by security forces.

Human rights advocates also criticize the country’s harsh emergency law, in place continuously since 1981, ostensibly to combat extremism.

Many say the security it provides also allows Egypt’s police forces to operate with total impunity, especially with political opponents of the regime.

Opposition members were hoping the plethora of political and economic problems facing many Egyptians would draw more protesters to the streets.

The “day of anger” also comes just two weeks after massive, countrywide protests in Tunisia, which eventually led to the ouster of strongman President Zine al-Abidine Ben Ali.

Most Egyptian political activists watched with glee as Ben Ali fled the authoritarian seat he held for 23 years.

The freshly energized opposition realizes the protests come at a critical point in Egypt's history.

Elections for the presidency are scheduled for September. Although the president has not announced whether he will run for a sixth term, Mubarak has long vowed to serve “until his last breath.”

But the health of the 82-year-old is rumored to be in decline. Having never named a vice president, public speculation over the future of the Egypt’s leadership has reached an all-time high.

Many in Egypt believe Mubarak’s son Gamal is being groomed for the job — Gamal has played a more visible role in the leadership of his father’s ruling National Democratic Party throughout the past decade.

Protesters fearful of the perceived plans for a nepotistic transfer of power in Egypt shouted anti-Gamal slogans on Tuesday.

But most of the anger was directed squarely at his father.

At least one of the many billboards displaying Mubarak’s image throughout the country was torn down, another rare occurrence in Egypt.