Zambian opposition leader Hakainde Hichilema who was arrested after failing to give right of way to President Edgar Lungu's convoy says he is in "good spirits", despite being kept in custody at a high security prison.

Writing on his Facebook page, Hichilema said: "We would like to assure you that we are alive and still in good spirits, despite numerous measures aimed at killing our spirit."

He added that Zambia's democracy was being "abrogated every day, but we can assure you that we are here to address this cancer that is eating the country alive while we watch".

Hichilema, a wealthy business, who was also the leader of the United Party for National Development (UPND), was recently charged with treason.

Authorities alleged that he blocked Lungu's motorcade with his own convoy of vehicles during a traditional ceremony in the country's western province in April.

They said that Hichilema's motorcade did not yield after presidential security guards signalled for it to get out of the way.

He was moved to a maximum security prison early this month and it was unclear when he would be back in court.