Former US president Jimmy Carter has returned to his volunteer work, a day after he was taken to hospital for dehydration while working with an organisation building homes for needy families.

A smiling Mr Carter showed up in jeans and a work shirt to the site in the St James neighbourhood of Winnipeg in Canada, where hundreds of Habitat for Humanity volunteers joined the former president and his wife Rosalynn to build 25 homes.

The 92-year-old was discharged on Friday morning from St Boniface General Hospital where he was treated "as a precaution" for dehydration, his spokeswoman Deanna Congileo said.

He then attended a prayer service at the work site.

"He and Mrs Carter extend their appreciation for the many well-wishes he received worldwide," Ms Congileo said.

Habitat for Humanity, which has had a long association with the Carters, is constructing 150 homes this year for people in need in Canada to celebrate the country's 150th anniversary.

The former president and his wife were in Edmonton, where Habitat is building 75 homes, from Monday to Wednesday before heading to Winnipeg.

Mr Carter had been working for about 90 minutes on Thursday morning when he went to sit down in a chair, the Winnipeg Free Press reported.

He appeared to wobble, so Secret Service agents led him to his motorcade. He was treated by paramedics who took him away in an ambulance, without using lights or siren, the newspaper said.

This week's project building houses in several Canadian communities is the 34th time the Carters have pitched in on Habitat projects, lending a hand - and their name - to promote the work.

Mr Carter was diagnosed with melanoma that had spread to his brain in 2015 but announced in March the following year that he no longer needed treatment.

He continued to volunteer for Habitat while being treated for cancer, working alongside volunteers at a home in Memphis in November 2015.

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