Seven scientists and other experts are standing trial on manslaughter charges for allegedly failing to sufficiently warn residents before a devastating earthquake that killed more than 300 people in central Italy in 2009.

The case is being closely watched by seismologists around the world, who insist it is impossible to predict earthquakes and say no major tremor has ever been foretold.

Last year about 5,200 international researchers signed a petition supporting their Italian colleagues, and the Seismological Society of America wrote to Italy's president expressing concern about what it called an unprecedented legal attack on science.

The seven defendants are accused of giving "inexact, incomplete and contradictory information" about whether smaller tremors felt by L'Aquila residents in the six months before the quake, on 6 April 2009, should have constituted grounds for a quake warning.

Specifically, prosecutors focused on a memo issued after a meeting on 31 March 2009 of the great risks commission, which was called because of mounting concerns about the months of seismic activity in the region.

According to the commission's memo – issued one week before the big quake – the experts concluded that it was "improbable" that there would be a major quake, though it added that one couldn't be excluded.

The 6.3-magnitude earthquake killed 308 people in and around the medieval town, which was largely reduced to rubble. Thousands of survivors lived in tent camps or temporary housing for months.