They may have different names according to the region they hit, but typhoons, hurricanes and cyclones are all violent tropical storms that can generate 10 times as much energy as the Hiroshima atomic bomb.

The typhoon that devastated the Philippines, wiping out entire towns with a death toll that could soar well over 10,000, is the Asian term for a low-pressure system that is called a hurricane in the Atlantic and northeast Pacific and a cyclone in the South Pacific and Indian Ocean.

But meteorologists use the term "tropical cyclone" when talking generally about these immensely powerful natural phenomena, which are divided into five categories according to the maximum sustained wind force and the scale of the potential damage they can inflict.

Super Typhoon Haiyan, which is now heading towards Vietnam, was a category 5 typhoon -- the highest level -- when it hit the Philippines, with maximum sustained winds estimated at 315 kilometres (196 miles) an hour, and gusts reaching 380 kilometres an hour, according to Japan's meteorological agency.

The winds are reported to be the strongest ever measured, and Haiyan could wrest the title of most powerful cyclone on record from Super Typhoon Tip, which ravaged Japan in 1979.

The Philippines endures a seemingly never-ending onslaught of deadly typhoons, earthquakes, volcano eruptions and other natural disasters.

Every year, some 20 super storms or typhoons hit the country, of the 80 or so that develop above tropical waters annually.

Cyclones are formed from simple thunderstorms at certain times of the year when the sea temperature is more than 26 degrees Celsius (79 Fahrenheit) down to a depth of 60 metres (200 feet).

Sucking up vast quantities of water, they often produce torrential rains and flooding resulting in major loss of life and property damage.

They also trigger large swells that move faster than the cyclone and are sometimes spotted up to 1,000 kilometres ahead of the powerful storm. The sea level can rise several metres.

These powerful weather formations can measure between 500 and 1,000 kilometres in diameter and have a relatively calm "eye" at the centre.

They weaken rapidly when they travel over land or colder ocean waters.

Cyclones are closely monitored by satellites, and specialised centres around the world -- in Miami, Tokyo, Honolulu and New Delhi -- track the super storms' trajectories under the coordination of the World Meteorological Organisation.