Questions about the structural integrity of a toppled 17-storey building have been raised, after it crumbled in a 6.4-magnitude earthquake Saturday morning in southern Taiwan that is known to have killed 18 people and injured 484 so far.

Images have been circulating online of cooking oil cans clearly visible in pillars of the collapsed Wei Guan Golden Dragon Building in Tainan City, which was built in 1989. Some are questioning whether the oil cans were used as shoddy filler material in the building's construction, and if this had a part to play in the building coming down in the quake.

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The oil cans clearly visible, with rescuers at the scene.

Interior minister, Chen Wei-zen, said an investigation has been launched into whether the building's developer had cut corners, but noted the building had not been listed as a dangerous structure before the quake.

Albeit an alarming sight, the cooking oil cans may not have been that much of a structural liability, a building technician told Taiwanese paper, Apple Daily. Tai Yun Fa said the metal oil cans are sometimes used in decorative pillars that aren't weight-bearing, and the light barrels can help reduce the overall weight of the building and benefit its structure.

About 171 people have been rescued from Wei Guan, according to Tainan's emergency center. By Sunday morning, rescuers continued to search for about 132 people still trapped inside.

The collapsed Wei Guan building. Image: Wally Santana/Associated Press

Wei Guan isn't the only building that came down Saturday; nine others in the city collapsed and five are tilted at an angle.

Earthquakes frequently rattle Taiwan, but most are minor and cause little or no damage. One of the largest quakes in recent history, a 7.6-magnitude event in central Taiwan in 1999, killed more than 2,300 people.

Additional reporting by The Associated Press.