It is inconceivable that in a time of national crisis, the lights remain off in the people's Parliament, the Democratic Alliance's (DA's) John Steenhuisen has said.

He said the decision by Standard and Poors Global Ratings Services to downgrade South Africa's sovereign credit rating to "junk status" emphasised the need for Speaker Baleka Mbete to reconvene Parliament.

Parliament is currently in recess until May.

"One of Parliament's key constitutional functions is 'scrutinising and overseeing executive action' and holding the executive to account. It is therefore incumbent on Mbete to call an urgent sitting of the House to debate the Motion of No Confidence proposed by the DA on 30 March."

Political parties have called for an urgent motion of no confidence in President Jacob Zuma, following his Cabinet reshuffle.

Mbete on Sunday said she would consult with the leader of government business, Cyril Ramaphosa, and African National Congress chief whip Jackson Mthembu before making a decision.

Steenhuisen said all that remained was for Mbete to schedule a sitting.

"The time has arrived for Mbete to put the institution of Parliament before the president she slavishly shielded from accountability during previous crises. She cannot be seen to be dithering - Zuma's recklessness is already costing South Africa dearly."

Zuma has come under fire after getting rid of finance minister Pravin Gordhan.