South African opposition politicians have tried to stop President Jacob Zuma from addressing parliament, repeatedly interrupting the proceedings to declare that he is unfit for office because of corruption allegations.

The raucous scene unfolded as police and military forces patrolled central Cape Town to guard against protesters who want Mr Zuma to quit.

While at least one group of protesters scuffled with police who blocked their path, the streets were mostly calm.

President Zuma is "rotten to the core," said Julius Malema, leader of the Economic Freedom Fighters, an opposition party.

Other opposition politicians described the president as a "scoundrel" and a "constitutional delinquent".

Mr Zuma, who was waiting to give an annual address on the economy and other national matters, is a politically weakened figure who has faced calls to resign even from factions of the ruling African National Congress party.

Some ANC members blame Mr Zuma's scandals for the party's poor performance in local elections in August, in which it lost control of several key metropolitan areas.

Critics condemned an announcement by President Zuma's office that 441 members of the military would assist police in maintaining order during the speech and the opening of parliament.

The military has previously deployed for the event, but the security operation was among the largest in recent years.

The hours leading up to Mr Zuma's speech featured the pomp associated with the annual opening of parliament, when dignitaries walk on a red carpet and pose for cameras in an impromptu fashion show.

Leaders of the Democratic Alliance, the biggest opposition party, posed in front of a banner recalling nearly 100 psychiatric patients who died last year in Gauteng, the country's most developed province.

Local officials had transferred the patients to non-governmental groups allegedly operating with invalid licenses.

President Zuma, who has expressed condolences to the families of the dead, has been under scrutiny for an allegedly improper relationship with the Guptas, a business family of Indian immigrants that has been accused of meddling in top government appointments.

The president has denied wrongdoing.

Mr Zuma, who took office in 2009, also reimbursed the state more than $500,000 US in a scandal over upgrades to his private home.