TAKING on a 90-day, 1200km trek covering the length of New Zealand's South Island would challenge anyone, but Bellingen nine-year-old Lucas Simon is taking it in his stride.

Together with dad John, Lucas is approaching the halfway mark of the journey, which combines fundraising for literacy charity Room to Read with spending time with dad on an adventure of a lifetime.

Far from slowing him down, John says it is often Lucas helping him through the 10-15km daily target.

"Lucas and I have walked about 450km so far, starting at Bluff and currently in Wanaka," John said.

"By the time people read this we will be beginning the next stage, walking from Wanaka to Lake Tekapo. Most of this will be through the Southern Alps and quite high, over 1200m."

The ambitious father and son have walked through snow, hail and high winds, sometimes in complete solitude but often being overwhelmed by the warm, encouraging welcome they get along the way.

"They have really embraced us both for the charity we chose (Room to Read) but I feel particularly because they strongly feel the walking with dad theme: spend time with your dad," John said.

During their six months of preparation for the walk, John encountered a mix of scepticism and support. But the progress they've made already shows that, while ambitious, the task is not impossible.

"Lucas is growing both in strength and in mind," John said.

"He can read maps, help write blogs, gut a fish, cast a fly, walk mountains whilst reciting his times tables and carry a pack.

"He rarely complains and many times pushes me to new levels."

To follow the journey or help Room to Read build libraries in developing countries, visit walkingwithdad.com.