Rescuers have battled rough seas to reach remote Indonesian islands pounded by a 10ft tsunami that swept away homes, killing at least 113 people.
Scores more are missing and information is only just beginning to trickle in from the sparsely populated surfing destination, so casualty numbers are expected to rise.
Mujiharto, who heads the health ministry's crisis centre, said a 10ft wave washed away hundreds of houses on Pagai and Silabu, part of the remote and sparsely populated Mentawai island chain.
Though hundreds of disaster officials have been unable to get to many of the villages on the Mentawai islands - reachable only by a 12-hour boat ride - they are preparing for the worst.
Indonesia, the world's largest archipelago, is prone to earthquakes and volcanic activity due to its location on the so-called Pacific Ring of Fire - a series of fault lines stretching from the Western Hemisphere through Japan and south-east Asia.
The fault that ruptured on Monday, running the length of the west coast of Sumatra island, also caused the 9.1-magnitude quake that unleashed a monster tsunami around the Indian Ocean in 2004, killing 230,000 people in a dozen countries.
The 7.7-magnitude quake that struck late on Monday just 13 miles beneath the ocean floor was followed by at least 14 aftershocks, the largest measuring 6.2, according to the US Geological Survey.
Many panicked residents fled to high ground and were too afraid to return home. That could account in part for the more than 500 people still missing, said Hendri Dori, a local parliamentarian who was overseeing a fact-finding missing. "We're trying to stay hopeful," he said.
Meanwhile, the country's most volatile volcano, Mount Merapi, 800 miles to the east, started to erupt at dusk on Tuesday as scientists warned that pressure building beneath its lava dome could trigger one of the most powerful blasts in years.