River Gum Primary School children sat down to enjoy the picture book Arthur with Casey Mayor turned guest reader Janet Halsall.

Now in its eighth year, the event celebrates and acknowledges the vital work being done in libraries, schools and communities around Australia to develop young people's literacy and numeracy skills.

Organisers estimated more than a quarter of a million children across Australia took part in this year's event.

Australian Library and Information Association executive director Sue Hutley says the event has grown significantly over the years.

"National Simultaneous Storytime offers children a chance to share in the magic of a wonderful story and in a moment in time with thousands of other children nationally.

"The event also focuses attention on fantastic Australian books, on literacy and on encouraging a love of books and reading in young Australians.''

The Pakenham and Cranbourne libraries also held simultaneous readings of Arthur.

Last week, work started on the Doveton library's $150,000 extension. It will receive a new entrance, an expanded public computer area, a community meeting area and extra toilet facilities.

The library will stay open during the works.