Rescue teams struggled in heavy rain on Thursday to find people trapped under debris after a powerful earthquake hit the Indonesian city of Padang, possibly killing thousands, Reuters reported.

The 7.6 magnitude quake struck the bustling port city of 900,000 people on Wednesday, toppling hundreds of buildings. Telephone connections were largely severed, making it hard for officials to work out the extent of destruction and loss of life.

"We need aid as soon as possible. We need food and medicine. Our houses have collapsed," said Siti, a resident of Padang, capital of West Sumatra province.

"There are people still trapped inside after their houses collapsed."

Health Minister Siti Fadillah Supari told reporters at an airport in Jakarta before leaving for Padang that the number of victims "could be more (than hundreds or thousands). I think it's more than thousands, if we look at how widespread the damage is. But we don't really know yet".

The national disaster agency put the confirmed death toll at 220. Officials said 500 houses had collapsed.

A second quake, of magnitude 6.8, hit another part of Sumatra island on Thursday, causing fresh panic, according to television reports. The second quake's epicentre -- inland and further to the southeast -- was 154 km (96 miles) northwest of Bengkulu, the U.S. Geological Survey said.

The area could not immediately be contacted.

A Reuters reporter at the partially collapsed Jamil hospital in Padang said there were at least 40 corpses on the ground. Many patients had been evacuated to the hospital's yard.

The reporter, whose own house collapsed, said some medical tents had been set up nearby but that many people who had gathered were still waiting for treatment.

A woman holding her dead baby cried for help: "My son is dead. My son is dead." TV footage showed troops carrying a woman on a stretcher, blood seeping from wounds on her legs and her body covered in dust.

Heavy rain hampered rescue efforts and officials said power had been cut in Padang, which lies on a coastal plain and is surrounded by steep mountains that stretch far inland.

Sumatra is one of the most seismically active parts of Asia.

A 9.15 magnitude quake, its epicentre 600 km (375 miles) northwest of Padang, caused the 2004 tsunami that killed 230,000 people in Indonesia and other Indian Ocean nations.