Tokyo ? A strong earthquake struck near islands in southwestern Japan today, prompting authorities to warn that the area could be hit by a small tsunami.

The quake with a preliminary magnitude of 6.7 came shortly after a 6.2 temblor hit. Both quakes struck near the island of Miyakojima, part of the Ryukyu islands chain that stretches southwest toward Taiwan, Japan’s Meteorological Agency said.

The Meteorological Agency issued a tsunami advisory after the second and larger quake, saying that islands in the area could be hit by waves as high 18 inches.

Authorities were still trying to determine whether the second quake had triggered a wave, said Yuji Nishimae, a Meteorological Agency official.

There were no immediate reports of injury or damage in either quake.