South Africa's army has been called in to protect hospitals from striking public sector workers.
More than a million civil servants began an indefinite strike on Wednesday, calling for higher wages.
Earlier, police fired rubber bullets and water cannon at crowds of strikers protesting outside a Soweto hospital.
Military doctors, nurses and soldiers have been deployed to three out of South Africa's nine provinces.
More unions joined in on the second day of industrial action.
Gauteng province's health minister said they were investigating whether the deaths overnight of five people in a hospital east of Johannesburg were linked to staff shortages because of the strike.
Unions affiliated with Cosatu, South Africa's main union federation, have been holding out for an 8.6% pay rise.
But South Africa's government says it can barely afford the 7% offer it has put on the table for the police, teachers, doctors and nurses.
President Jacob Zuma has condemned the union's threat of violence against non-striking workers and said the government reserved the right to fire the strikers.
"If you declare a strike in that manner and you can't sit for a year without the kids going to school," he is quoted by the South African Broadcasting Corporation as saying.
"If the time goes, it means the government will have to take other actions."
"The [SA National Defence Force] has been instructed to render support to any government department that may require assistance during the public service strike," South Africa Press Association quoted defence ministry spokesman Ndivhuwo Wa Ha Mabaya as saying.
The BBC's Jonah Fisher in Johannesburg says the conditions at South Africa's hospitals have been causing the most concern to the authorities.
Many health workers who are not taking part in the strike have found themselves targeted by union members, he says.
Access to hospitals has been blocked - and on several occasions those on strike have gone into wards and dragged nurses away from their patients, our correspondent says.
Military armoured vehicles have been now deployed inside some hospital premises.
When rowdy strikers in Soweto stopped patients from entering the hospital grounds on Thursday morning, the police - forbidden by law from joining the strike - moved in.
Police spokeswoman Captain Nondumiso Mpantsha said the protesters were also trying to force their way in to picket inside the Chris Hani Baragwanath Hospital.
"Police had to use minimum force and fire rubber bullets to disperse the crowd... there is a heavy police presence at the scene," she told the BBC
Johannesburg's Eyewitness news website reported that a police helicopter was flying over the city's main Helen Joseph Hospital.
There have also been reports of intimidation at schools and teachers have threatened to disrupt classes at private schools.
But police stopped protesters planning to block one of the busiest motorways in Johannesburg on Thursday.