Venezuela's leftist leadership has called for a massive show of support for ailing President Hugo Chavez in Caracas on Thursday - the day he is supposed to be sworn in to a new six year term in office.

National Assembly speaker Diosdado Cabello said on Tuesday that a huge rally would be held that day to show the public's support for Chavez.

"All of Venezuela will come here in front of the Miraflores presidential palace, the people supporting our president, the people supporting comandante Chavez - in an overwhelming manner, the people in the street," he said.

A rising storm of criticism has greeted plans to indefinitely delay Chavez's inauguration if the cancer-stricken leader is too sick to participate, with the nation's Catholic church the latest group to wade into the row.

Cabello, who also heads Chavez's United Socialist Party of Venezuela, defended the plan as constitutional, and said heads of state and government were also expected to attend the giant rally.

Chavez, the communist firebrand and adversary of the US, underwent his fourth round of cancer surgery in Havana nearly a month ago, and is suffering from a severe pulmonary infection that has caused respiratory difficulties.

Information Minister Ernesto Villegas said late on Monday that Chavez's health condition has remained "stationary" since the latest complication from surgery was reported four days ago.

Uruguay's President Jose Mujica confirmed that he would be in Caracas.

The government, meanwhile, also gained support from Latin American heavyweight Brazil, which said a constitutional process was in place to assure continuity for up to 180 days in the event Chavez is unable to be sworn in.

But the Catholic church entered the controversy for the first time, with a veiled warning to the government that it would be "morally unacceptable" to override the constitution, noting that Chavez's prolonged absence had put the country's stability at risk.

A key opposition figure on Sunday called for demonstrations if the government pushes past the January 10 date without Chavez being sworn in.

The Venezuelan president, 58, has not been seen in public since he underwent his latest surgery. It is his longest absence during 14 years in power.