JAKARTA, Indonesia — A powerful earthquake shook western Indonesia for the second straight day today and triggered a tsunami alert. The latest tremor was also felt in neighboring Singapore, causing tall buildings to sway.

Yesterday, a strong earthquake shook Southeast Asia, collapsing buildings, killing at least five people, and injuring dozens in Indonesia. That tremor triggered small waves off the coastal town of Padang in Sumatra, the island ravaged by the 2004 tsunami disaster.

The U.S. Geological Survey said today’s tremor had a preliminary magnitude of 7.5 and was 125 miles from Bengkulu, a city on Sumatra, at a depth of six miles. Local officials said it had the potential to trigger a tsunami.

After yesterday’s 8.4-magnitude quake, frightened people fled their homes and ran inland, fearing a repeat of the 2004 earthquake and tsunami that struck a dozen nations around the Indian Ocean, killing an estimated 230,000 people.

“Everyone is running out of their houses in every direction,” Wati Said reported by cell phone from Bengkulu, a town 80 miles from the quake’s epicenter. “We think our neighborhood is high enough. God willing, if the water comes, it will not touch us here. … Everyone is afraid.”