Scientists have measured a wind speed of 318 mph (509km/h) inside a tornado that recently struck Oklahoma City - the fastest wind speed ever recorded on Earth.

Watch this report on impact of the tornado

Until recently it was not thought that such a wind speed was possible.

The previous fastest measured speed was 286 mph (458 km/h). That was also measured in a tornado in Oklahoma.

The fastest non-tornado wind ever recorded was is 231 mph (370 km/h), measured at Mount Washington in New Hampshire in 1934.

By comparison, the wind that ravaged the southern part of the United Kingdom in October 1987 was estimated to be less than 100 mph (160 km/h).

Radar measure

The wind speeds could not be measured by conventional means

A team led by Joshua Wurman of the University of Oklahoma used a truck-mounted Doppler radar system. This measures the speed of raindrops inside a storm, and provides an estimate of the wind speed.

It is not possible to measure such wind speed using conventional devices, as they cannot withstand such powerful tornadoes.

Scientists say that the record-setting wind speed probably occurred a few hundred feet (in the region of 100 to 200 metres) above the ground.

Winds that powerful can rip the tarmac from the roads, tear the grass from the ground and toss cars around like toys.

Close to maximum rating

The Oklahoma tornado - which killed four people and destroyed over 250 homes - was classified as an F-5 on the 0 to 6 Fujita scale.

No tornado has ever been classified as an F-6, but a speed of 318 mph (509 km/h) would put the tornado only 1 mph (1.6 km/h) below the maximum F-6 rating.

The ability to make such measurements is a breakthrough in tornado research.

Scientists will soon have a much better picture of the inner workings of a tornado.