Photo gallery: US braces for Hurricane Sandy, thousands of flights cancelled

WASHINGTON (AFP) - President Barack Obama warned Americans on Sunday to take Hurricane Sandy "very seriously" as authorities prepared a virtual shutdown of the Eastern Seaboard due to the impending mega-storm.

More than 5,000 flights out of East Coast hubs were cancelled and ground transport was due to grind to a halt on Monday as non-essential government staff were told not to show up for work and public schools were closed.