Former South African president Jacob Zuma's personal assistant at the African National Congress (ANC) received a phone call threatening Zuma and his family with death, the State capture commission of inquiry heard on Tuesday.

"My PA at the ANC side was called by an unknown person who told her to inform me that he would kill me and my family. I am putting this on record because I'll come back to this issue later... the plan [to kill me] has been implemented already. Not only that...my senior advocate [Muzi] Sikhakhane was also threatened not long ago. I lost a child once, I know what this can do," the former president said on his second day before the inquiry.

Zuma had on Monday told the Zondo-led commission that the plot to kill him was hatched decades ago when he was chief of intelligence at the ANC because "he knew too much." 

He said he has survived death threats and poisoning as some within his organisation, working with foreign intelligence agencies, are hellbent on getting rid of him.

Commission chairperson Deputy Chief Justice Raymond Zondo condemned threats against anyone, including witnesses appearing before him.

"I would like to say it is totally unacceptable for anyone in society to want to use violence, intimidation and all kinds of illegal means when they're unhappy about anybody, because our legal system is such that people can go to police and courts if they have complains against others," said Zondo. 

"When threats are made concerning a person giving evidence, people who come to the commission could feel threatened or intimidated along with their families. I am happy that whatever threat has been made has not stopped Mr Zuma to give evidence... but all steps should be taken to ensure that no one threat is undertaken. Mr Sikhakhane is a lawyer and lawyers represent clients... they're just doing their job."

The commission has set aside this week to hear Zuma's testimony. 

His first day at the commission included Zuma presenting an opening statement that lasted over an hour, in which he claimed there were plots to kill him and how he and his family suffered continued public attacks for decades.