Local residents take shelter at the Pedro Menendez high school in St. Augustine, Florida, on October 6, 2016, ahead of Hurricane Matthew

From a special storm website created by a US military agency to a state's interactive map of evacuation routes, the authorities are mobilizing digital tools to help millions of people cope with the devastating passage of Hurricane Matthew.

The US Army's National Geospatial-Intelligence Agency has created a site dedicated specially to Matthew (nga.maps.arcgis.com).

The site says the NGA "will be working directly with federal, state and local organizations to assist" in hurricane response, including "essential information to protect and secure lives and infrastructure." No password is required.

Matthew gained strength early Thursday to become a powerful Category 4 hurricane, with of 140 miles (220 kilometers) per hour.

Current forecasts show it pummeling southeast Florida with its full force Thursday night and then moving up the US eastern coast to the Carolinas, before possibly veering back out to sea.

The NGA website will catalog areas of flooding, road and bridge closings, damages to buildings, mudslides, and possible landing areas for rescue helicopters.

In South Carolina, a Transportation Department website (www.scdot.org/getting/Matthewresources.aspx) includes an of evacuation routes, with travel-time estimates, plans to reverse directions on some highways, and road-conditions updates.

The site calls on all travelers to exercise "extreme caution."

More than two million Americans have been urged to evacuate the southeast coast as the hurricane approaches. Matthew has gained strength after its devastating passage over Haiti left at least 108 people dead.