South African President Cyril Ramaphosa on Friday returned early from a summit in London to rush to the scene of violent demonstrations in North West province, where at least 23 people have been arrested.

Ramaphosa, who took power in February, expressed "serious concern" over the clashes between police and protesters, and called for calm as he faced one of the first major challenges of his presidency.

Violent protests are common in South Africa, but North West province has been a hotbed of unrest due to boiling frustration over lack of housing, health services and jobs.

Television images showed police firing rubber bullets on Friday morning to break up crowds of protesters in Mahikeng, the provincial capital, shortly before Ramaphosa was due to arrive.

Footage from Thursday showed thick smoke rising into the air in and around the city, while protesters looted shops and burned vehicles overnight.

Ramaphosa called in a statement for "all aggrieved parties to express their grievances through peaceful means and engagement rather than violence and anarchy."

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He also urged security forces to "exercise maximum restraint".

Local media said one person was thought to have died in the demonstrations, which erupted earlier this week.

The trigger for the unrest was reportedly the death on Tuesday of two patients at a health clinic that was closed due to a month-long dispute over health workers' salaries and contracts.

- Anger over graft -

Much of the anger has been directed at Supra Mahumapelo, the provincial premier, who is accused of involvement in the government graft scandals that have engulfed the ruling ANC (African National Congress) party.

The border to neighbouring Botswana was closed due to the violence, according to Botswanan officials, while schools, shops, offices and government services across North West province were shut on Friday.

"We are doing our best to keep the situation under control," police spokesman Sabata Mokgwabone told ENCA television. "We asked for reinforcement from other provinces and head offices."

Ramaphosa had been attending the Commonwealth Heads of Government Meeting in London where he was leading a government delegation.

He was due to address an urgent meeting in Mahikeng at 12pm (1000 GMT) alongside other senior ANC officials.

- New leadership -

Ramaphosa, who took over as leader of the ruling African National Congress in December, replaced Jacob Zuma as national president earlier this year.

Zuma's nine-year tenure saddled South Africa with weak growth, ballooning national debt, depressed investor confidence and record unemployment.

The ANC forced Zuma from office in February largely due to his mounting legal challenges and multiple corruption scandals, and the party has distanced itself from its former leader.

Ramaphosa has vowed to crack down on government corruption, which he has admitted is a serious problem, and improve South Africa's ability to attract foreign investment.

Unemployment is at a record high of about 28 percent, with youth unemployment reaching over 50 percent in many areas.

Zuma appeared in court earlier this month at a preliminary hearing on graft charges that he denies.