Tens of thousands of South African construction workers downed tools on Monday, adding to strike chaos that has crippled output and disrupted air traffic while fanning fears of new violence.
The some 90,000 construction workers embarked on an indefinite strike demanding a 13 percent pay increase against an offer of six percent made by their bosses.
Two people were reportedly stabbed in an incident related to the construction strike in Johannesburg's plush suburb of Sandton, police told the SAPA news agency.
The South African government warned the strikers to stay "within the ambit of the law", adding that "those that contravene the country's laws will face the full might of the law."
It added: "It is unacceptable when people's rights are violated by perpetrators of violent actions, such as inflicting injury or death to other persons, damage to property and the destruction of valuable public infrastructure."
Labour disputes last year claimed up to 50 lives at South Africa's platinum mines, with 34 miners shot dead by police in a crackdown on a single day.
Also Monday, 1,300 aircraft maintenance technicians launched a stayaway, demanding a 12 percent pay rise, Vincent Masoga, spokesman for the South African Transport and Allied Union, told AFP.
The technicians repair and service aircraft for South African Airways and other domestic and international carriers, including British Airways and Qantas.
The strike has so far caused minor disruption, including an arrival delay for the national rugby team returning from Argentina.
But the Airports Company of South Africa denied that delays at Johannesburg's OR Tambo airport were related to the strike.
Meanwhile, as many as 30,000 auto workers have been on strike for a week, and more strikes are in the pipeline -- in the gold mining and textile sectors -- at a time of year when annual wage negotiations take place in South Africa.
Around 120,000 gold mine workers on Saturday gave a week's notice to stage a strike over salaries if no deal is reached with the mining firms this week.
The government statement urged employers and workers to "engage in meaningful dialogue and to speedily reach an agreement".
It urged "government and the citizens of the country... to work together in a peaceful and stable manner to address the underlying challenges of poverty, unemployment and inequality."