Port-Au-Prince, Haiti (CNN) -- With expectations of change running high, former bad-boy pop star Michel Martelly was sworn in Saturday as the president of impoverished Haiti, still reeling from last year's devastating earthquake.

In a sign of the nation's troubles, the electricity went out moments before the inauguration, prompting formally dressed dignitaries and guests -- including former U.S. President Bill Clinton and French Foreign Minister Alain Juppe -- to fan themselves to stave off rising May heat.

Immediately, Twitter lit up with posts calling the blackout a "bad sign." Despite the outage, the ceremony proceeded before parliament and Martelly took his oath of office amid the lights of media cameras.

Martelly, savvy in social media, tweeted his own inauguration as Haiti's 56th president minutes after it happened along with a flurry of messages expressing hope that change would now come to Haiti.

Outside, thousands of Haitians rejoiced at what they see as a new start for their country, where many people remain displaced from their homes and post-quake reconstruction has been slow, one of the reasons popular discontent with the former administration had grown.

The collective joy surfaced in a nation that has been subjected to months of misery compounded by a cholera epidemic that erupted last October. Port-au-Prince was under strict security all day Saturday, with United Nations peacekeepers out in force on street corners.

"Today is a big day for us," said Jolina Desroches, 40. "Before, (Martelly) was just the president of Kompa (a Haitian musical genre). Today, he is the president of the Haitian people."

Dressed in a dark suit and red tie, Martelly stepped outside after the ceremony draped in the presidential sash. Supporters hoping for a glimpse of the new president climbed up flag polls over the United Nations plaza where the ceremony took place and pressed against barriers, as vendors took advantage of the crowd to sell plantain chips and bananas.

After attending a lengthy Roman Catholic Mass in his honor, Martelly made his first speech as president on Saturday afternoon from a temporary stage in front of the collapsed National Palace, an iconic symbol of Haiti's struggles.

He promised change, emphasizing the need to improve public safety to facilitate investment -- saying that, "with insecurity, the country cannot work. ... Money cannot (stay in the system), which means there isn't work and the misery is worse." The new president also reaffirmed his campaign promise to offer free education to young Haitians.

The entire address was in Creole, except for one part seemingly aimed at encouraging the international community to come to and invest in the Caribbean nation: "A new Haiti (is) open for business now!"

Thousands who had gathered outside the palace gates -- where a massive tent city still fills the capital's central plaza, as it has since the epic earthquake -- cheered the president's remarks.

Martelly has acknowledged his task as herculean in nature. He has pledged to fight corruption and institute measures of transparency.

He told CNN last month that one of his first actions as president would be to nominate high court judges. Creating an independent judiciary will send an important signal, he said.

"We have to establish a rule of law," he said. "We want justice for everyone."

Martelly also vowed to end government corruption that has plagued Haiti for years.

"I am excited to take command and make the right decisions for my country," he said during a visit to Washington in April.

In a message posted on Twitter after the inauguration, the U.S. Embassy in Port-au-Prince said it was looking forward to working with the new government to achieve a better future for Haitian people.

Martelly's candidacy was unexpected -- he was better known as Sweet Micky, the kompa singer with flamboyant stage presence, but appealed to voters who had grown weary with the status quo.

CNN's Moni Basu and Gary Tuchman and journalist Allyn Gaestel contributed to this report.