Zohra Yousuf who heads the Human Rights Commission of Pakistan (HRCP) said the 800 people were victims of often targeted and violent shootings in the last seven months.
"The figures are a cause of great concern for every law abiding Pakistani," she said.
Previously the HRCP had put the figure of those killed in the violence in Karachi in the first six months of the year to around 500 but in one of the bloodiest months witnessed by the city another 300 people were killed in July.
Yousuf said the figures compiled by the HRCP staff also through police records showed that around 300 people were killed in July.
The figures represent a big challenge for the government which has already deployed an additional force of 1000 Frontier Constabulary (FC) soldiers in the city to assist the police and para-military rangers to control the violence.
Around 60 people were killed in the cycle of violence and in arson attacks in the last five days this week.
The HRCP official said the violence in Karachi is the deadliest since 1995, when more than 900 killings were reported in the first half of the year.
Meanwhile the Muttahida Qaumi Movement which is the largest part in Karachi and represents the Urdu speaking Muhajirs who migrated at partition from India has demanded a judicial inquiry into the violence and killings.