The unfolding secret story of the 9/11 attacks on the World Trade Centre and the Pentagon is being told today when more than 500,000 intercepted pager messages, many from US officials, are published online in the order in which they were sent.

The mass live leak began at 8am GMT and will continue for 24 hours until all of the messages are seen as they were sent on September 11.

The experiment by whistleblowing website Wikileaks includes pager messages sent on the day by officials in the Pentagon, the New York police and witnesses to the collapse of the twin towers.

Wikileaks said the messages would show a "completely objective record of the defining moment of our time".

It added: "We hope that its entry into the historical record will lead to a more nuanced understanding of how this tragedy and its aftermath may have been prevented."

The post said the release of the messages at times corresponding to when they were sent would help "foster a deeper understanding".

A preview of some of the messages to be leaked suggests they show how panic and rumour began to spread on the day, and are likely to fuel conspiracy theories about the attacks.

One message from a New York City official sent just minutes after the first attack said: "WTC has been hit by an airplane and a bomb." Another says: "It's reported that a US military helicopter circled the building then crashed into or next to the Pentagon." Later in the day, a message presciently says: "We are bombing Afghanistan."

One message from a witness reads: "Still in my apt, nowhere to go ... This is the end of the world as we know it."

Wikileaks would not reveal the source for the leak, but hinted: "It is clear that the information comes from an organisation which has been intercepting and archiving US national telecommunciations since prior to 9/11.

Wikileaks has a good track record in releasing authentic official documents, but its website tends to get overloaded at busy times. It is encouraging readers to follow the leaks on Twitter.