Hurricane Florence is packing maximum sustained wind speeds of 120 miles per hour, while Mangkhut is packing maximum sustained winds of 135 miles per hour, according to the Joint Typhoon Warning Center (JTWC) and the NHC.
It can affect as many as 31.4 million people in the region, according to the United Nation's Global Disaster Alert and Coordination System.
Mangkhut has gathered strength since it struck the U.S. Pacific territories of Guam and the Northern Mariana islands overnight on Monday, tearing down trees and power lines and leaving hundreds of people homeless.
Governor Manuel Mamba of the Philippines island of Cagayan said officials would start evacuating islanders on Thursday.
A super typhoon roared toward the Philippines on Thursday, prompting thousands to evacuate ahead of its heavy rains and fierce winds that are set to strike at the weekend before moving on to China. According to HKO, the storm is expected to skirt around 100 to 200 kilometers (62 to 124 miles) south of Hong Kong on Wednesday afternoon, bringing strong winds and rain.
With the predicted path of the typhoon, it could also hit Taiwan and Hong Kong next.
This places Typhoon Mangkhut as the strongest tropical storm for decades.
The civil defence office in Manila said towns and cities on Mangkhut's path are preparing government buildings as evacuation centres, stockpiling food and other emergency rations. The threat to agriculture comes as the Philippines tries to cope with rice shortages.
A missile test aboard a navy ship to be attended by President Rodrigo Duterte off northern Bataan province was cancelled due to the approaching typhoon.
Although there are still uncertainties about its trajectory, it is expected that Mangkhut will bring adverse weather to the regions of Macau, Hong Kong and the coastal cities of southern China.
TYPHOON MANGKHUT, which will be locally named Ompong once it enters the Philippine Area of Responsibility (PAR), has intensified as it moves westward towards the northern part of the country.
Mangkhut is the 15th storm this year to batter the Philippines, which is hit by about 20 storms a year and is considered one of the world's most disaster-prone countries.
Meanwhile, the USA east coast braces as Hurricane Florence barrels towards the Carolinas, expected to make landfall late September 14 or early September 15.