A magnitude-7.3 earthquake hit the waters off Hualien in China's Taiwan region on Wednesday. The quake was followed within 40 minutes by two aftershocks of magnitude-6.0 and magnitude-5.9, according to China Earthquake Networks Center. It is said to be the strongest quake to hit the island in 25 years and authorities have issued a tsunami warning. According to local media reports, strong tremors were felt in various parts of Taiwan, prompting Taipei's metro system to halt operations for 40 to 60 minutes.