HARARE, Zimbabwe (AP) — Zimbabwe's main opposition party said Tuesday its leader was in a hospital in neighboring South Africa as concerns rise over the health of Morgan Tsvangirai, who has dominated the opposition for close to two decades.

Spokesman Luke Tamborinyoka said the former prime minister is in Johannesburg for cancer treatment. Tsvangirai in 2016 announced he had colon cancer, and he has come in South Africa for treatment in the past.

"I am shocked to read in the press that I am in a critical condition," his Twitter feed said Tuesday. "Of course I have cancer and not feeling too well but I am stable and the process is under control."

Tamborinyoka said the 65-year-old still hopes to lead the opposition into elections scheduled for no later than August.

Tsvangirai's condition appeared to have deteriorated when he met new President Emmerson Mnangagwa in January. His absence has fuelled infighting among MDC party officials interested in succeeding him.

Tsvangirai has been the main challenger to the ruling ZANU-PF party since 1999, when he formed the MDC party. He shared power for a few uncomfortable years with former President Robert Mugabe, who resigned in November under pressure from the military and ruling party.