BBC correspondent Andy Gallacher: "Pinera has a huge job on his hands"
Sebastian Pinera has been sworn in as president of Chile, minutes after it was hit by the largest aftershock since last month's devastating earthquake.
The 6.9-magnitude tremor was centred in O'Higgins Region, some 140km (90 miles) south of the city of Valparaiso, where the inauguration ceremony took place.
The congress building was evacuated soon after. On taking office, Mr Pinera said: "It's time to get to work."
His presidency ends two decades of left-wing rule in Chile.
The tycoon not only faces the challenge of reconstruction, but takes over from the highly popular Michelle Bachelet, who was the country's first woman president.
Ms Bachelet left office with an 84% popularity rating despite criticism of her government's response to February's 8.8-magnitude earthquake and ensuing tsunami, which left close to 500 people dead.
I'm leaving office with sadness for the suffering of our people, but also with my head held high
Michelle Bachelet Outgoing president
Earlier, Chile's disaster management chief resigned, six days after the head of the navy's oceanography service was dismissed for failing to provide a clear warning of the tsunami.
A BBC correspondent in the capital, Santiago, says buildings there shook and people rushed out onto the streets after Thursday's tremor, but no damage was reported.
A tsunami alert was issued for a long stretch of Chile's coast but was later lifted, except for Easter Island, where it remained in effect.
The US Pacific Tsunami Warning Center said the aftershocks were too small to cause "a destructive widespread tsunami".
Mr Pinera said there had been "significant damage" in Rancagua, a city almost 100km (62 miles) south of the capital, which was close to the main tremor's epicentre, but there were no immediate reports of injuries.
The US Geological Survey initially estimated the largest aftershock's magnitude at 7.2, but later revised it down to 6.9. It was followed by more tremors, the biggest of which had a magnitude of 6.7.
The inauguration ceremony in the port city of Valparaiso, which houses the National Congress, was intended to be an austere affair.
The planned dinner was cancelled and the whole event scaled back out of respect for victims of the quake.
Ms Bachelet, who was constitutionally barred from seeking re-election, handed the red, white and blue presidential sash to Mr Pinera.
"I'm leaving office with sadness for the suffering of our people, but also with my head held high, satisfied with what we have accomplished," she said in her farewell address.
The leaders of Peru, Colombia, Argentina and Bolivia were among the dignitaries to attend the inauguration.
The 6.9 magnitude aftershock sparked fears of another tsunami
Seldom can an incoming president have faced such a massive and immediate challenge, says the BBC's Gideon Long in Santiago.
Many people have been made homeless by the quake, with about half a million homes destroyed.
BBC reader Ian Hutcheon, from San Vicente, 45km south of Rancagua, described Thursday's aftershock as "very severe".
"I was in a bank when it hit and there was mayhem, panic and chaos," he said.
"We won't be the government of the earthquake, we'll be the government of reconstruction," Mr Pinera said recently.
Last month, Mr Pinera named his cabinet, leaving out any figures linked with the former military ruler, Augusto Pinochet.
In his election campaign, the 60-year-old the conservative leader said he would focus on boosting economic growth and producing jobs while continuing with the outgoing president's social policies.
Mr Pinera is one of the country's richest men.
He made his fortune introducing credit cards to Chile, then went on to buy a television channel, a stake in Chile's most successful football club, and put millions of dollars into other investments.
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