Within hours of the swearing in, looters descended on the headquarters of Sierra Leone People's party (SLPP), ransacking rooms and carting away furniture and equipment, posters and coat racks.
Police shot live rounds into the air and arrested several looters before the area was cordoned off.
During the swearing in on Monday, Koroma, who won 55 per cent of votes in the tense run-off election held earlier this month, vowed to fight corruption and increase jobs.
Vice-president Solomon Berewa, the losing SLPP candidate, obtained 45 per cent of the 1.7 million votes.
|Koroma vowed "zero tolerance" on graft and |
mismanagement of state resources [Reuters]
Berewa and outgoing president, Ahmed Tejan Kabbah, who was legally barred from running for a third five-year term, were present at the ceremony.
"I inherited a bankrupt, war-torn and failing state. Today, I am handing over to you a fully stable and functional state," Kabbah told Koroma.
Thousands of Koroma's All People's Congress (APC) supporters, donning red T-shirts and hats, clogged the streets of Freetown, singing and dancing throughout a heavy downpour.
Ruling party officials had earlier decried the outcome of the election which was marred by allegations of fraud.
Last month's election was Sierra Leone's first presidential vote since UN peacekeepers withdrew two years ago.
Tens of thousands of civilians died or were left without limbs after years of civil war fuelled by corruption and financed by illegal "blood diamonds".
Koroma, a former insurance company executive, vowed to govern with the efficiency of a business, promising to quickly rebuild roads and war-battered infrastructure.
"My government will spare no effort to adopt zero tolerance on corruption and mismanagement of state resources," he said. "We know how high your expectations are and that you have suffered for too long."
The APC, which also won the majority of legislative seats in last month's vote, was last in power between 1967 and 1992, ruling with strong-arm tactics that helped foment discontent and fuel rebellion.
Despite Koroma's pledge for reform, many in Sierra Leone fear the same will happen again.
In New York, the UN pledged continued support for the newly-elected government.
Michele Montas, the spokeswoman for Ban Ki-moon, the UN secretary-general, said he commended the people "for exercising patience and restraint during the tallying of the vote".
In 2002, UN forces helped re-establish peace but most of Sierra Leone's citizens remain poor and unemployed, and corruption is rampant.