Millions of people in the northern hemisphere are set to be smashed by strong winds, rain and flooding from typhoons and hurricanes later this week.

This afternoon, Typhoon Mangkhut hit the coast of Guam, generating wind gusts of 215kmph at its core.

It is expected to increase in size and strength as it passes through the Mariana Islands tonight and will produce heavy rain, flooding and very destructive winds.

Florence, Isaac and Helene (L-R) are strengthening as they move across the Atlantic. (Supplied)

Typhoon Mangkhut is forecast to move further west, strengthening as it reaches the Phillippines and Taiwan toward the end of the week.

According to the Typhoon Warning Centre, wind gusts may reach close to 300kmph near the typhoon’s core when it hits the region on Saturday.

Another three typhoons are currently strengthening over the Atlantic Ocean.

The strongest of the three systems, Hurricane Florence, is currently a category one.

Hurricane Florence is making its way to America's East Coast. (Supplied)

It is forecast to intensify into a category four or five tropical cyclone in the next 24 hours and is expected to reach the US East Coast by Thursday.

“Make your plans now,” South Carolina Governor Henry McMaster urged residents yesterday.

“Presume that a major hurricane is going to hit right smack dab in the middle of South Carolina.”

He also said he had asked US President Trump to declare a state of emergency in South Carolina in preparation for the storm’s arrival.

Typhoon Mangkhut is strengthening as it approaches the Phillippines. (Supplied)

The US National Hurricane Centre is also tracking Hurricane Isaac and Hurricane Helene as they approach from the Atlantic Ocean.

Hurricane Isaac is expected to reach the Caribbean in the next day or so and already has maximum winds of 120kmph.