PADANG, Indonesia - A powerful earthquake struck off the city of Padang on Indonesia's Sumatra island Wednesday, killing at least 75 people and trapping thousands under rubble, officials said.

The death toll was likely to rise as many buildings in the city of 900,000 people had collapsed, Vice President Jusuf Kalla told a late night news conference in Jakarta.

We have received a report from the mayor of Padang that the death toll is 75. But many others are trapped in collapsed shops, building and hotels. It is difficult to know because it is dark now, Kalla said.

TV footage showed devastation, with piles of rubble and smashed houses after the 7.6 magnitude earthquake, which caused widespread panic across the city.

Rustam Pakaya, the head of the health ministry's disaster center in Jakarta, said thousands of people are trapped in the rubble of buildings.

The main hospital had collapsed, roads were cut by landslides and Metro Television said the roof of Padang airport had caved in. Thousands were expected to spend the night in the open while a full assessment of the damage would need to wait until daybreak.

The disaster is the latest in a spate of natural and man-made calamities to hit Indonesia, a sprawling archipelago of 226 million people.

Kalla said the government was preparing for an emergency response of up to two months.

Welfare Minister Aburizal Bakrie said authorities should prepare for the worst, adding damage could be on a par with an earthquake in the central Java city of Yogyakarta in 2006 that killed 5,000 people and damaged or destroyed 150,000 homes.

The quake was felt around the region, with some high-rise buildings in Singapore, 440 km (275 miles) to the northeast, evacuating staff. Office buildings also shook in the Malaysian capital, Kuala Lumpur.

The Pacific Tsunami Warning Center canceled an earlier tsunami alert.

Hundreds of houses have been damaged along the road. There are some fires, bridges are cut and there is extreme panic here, said a Reuters witness in the city, who also said broken water pipes had triggered flooding.

His mobile phone was then cut off and officials said power had been severed in the city. A resident called Adi later told Metro Television there was devastation around him.

For now I can't see dead bodies, just collapsed houses. Some half destroyed, others completely. People are standing around too scared to go back inside. They fear a tsunami, said Adi.

No help has arrived yet. I can see small children standing around carrying blankets. Some people are looking for relatives but all the lights have gone out completely.

A series of tsunamis earlier on Wednesday smashed into the Pacific island nations of American and Western Samoa, and Tonga killing possibly more than 100 people, some washed out to sea, destroying villages and injuring hundreds.

Geologists have long said Padang may one day be destroyed by a huge earthquake because of its location.

Padang sits right in front of the area with the greatest potential for an 8.9 magnitude earthquake, said Danny Hilman Natawidjaja, a geologist at the Indonesian Science Institute, in February.

The entire city could drown in a tsunami triggered by such a quake, he warned.

Several earthquake-prone parts of the country hold tsunami practice drills, and the national disaster service sends alerts via telephone text messages to subscribers.

But some experts have long said Indonesia needs to do more to reduce the risk of catastrophe.

(Additional reporting by Telly Nathalia and Sunanda Creagh in Jakarta; Writing by Nick Macfie/Ed Davies; Editing by Dean Yates)

Tsunami Earthquake Quake