Sebastian Pinera has been sworn in as president of Chile, minutes after it was hit by the largest aftershock since last month's devastating¹ earthquake.

塞巴斯蒂安·皮涅拉宣誓就职智利总统几分钟之后，智利即遭受自上月大地震之后规模最大的一次余震。

BBC correspondent Andy Gallacher: "Pinera has a huge job on his hands"

The 6.9-magnitude tremor²（颤动，震颤） was centred in O'Higgins Region, some 140km (90 miles) south of the city of Valparaiso, where the inauguration³ ceremony（就职典礼） took place.

The congress building was evacuated⁴（疏散，撤离） soon after. On taking office, Mr Pinera said: "It's time to get to work."

His presidency⁵ ends two decades of left-wing rule in Chile.

The tycoon⁶ not only faces the challenge of reconstruction⁷, 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（接踵而至的） tsunami⁸, which left close to 500 people dead.

Earlier, Chile's disaster management chief resigned, six days after the head of the navy's oceanography（海洋学） service was dismissed（解雇） 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（震中） , but there were no immediate⁹ reports of injuries.

The US Geological Survey initially¹⁰ estimated the largest aftershock's magnitude at 7.2, but later revised it down to 6.9. It was followed by more tremors¹¹, the biggest of which had a magnitude of 6.7.

'Massive challenge'

The inauguration ceremony in the port city of Valparaiso, which houses the National Congress, was intended to be an austere¹²（朴素的，严格的） affair.

The planned dinner was cancelled and the whole event scaled back（响应缩减） 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（肩带，腰带） 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（高官，显要人物） to attend the inauguration.

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.