WINNIPEG (REUTERS) - It was shortly after his arrival at a Habitat for Humanity house-building project in Winnipeg, Canada, that former United States president Jimmy Carter fell ill.

Habitat for Humanity's Jonathan Reckford says Mr Carter was affected by the summer heat.

"President Carter was dehydrated working in the hot sun. President Carter told us he's ok and is being taken offsite for observation. He encourages everyone to stay hydrated and to keep building," said Mr Reckford.

Eyewitnesses said the 92-year-old became unsteady at a construction site and slumped over a chair after working on a home for more than an hour.

He was taken to St Boniface General Hospital for treatment. His wife Rosalynn was with him throughout.

The peanut farmer from Georgia has lived longer after his term in office than any other president in US history and is still extremely active with Habitat for humanity.