The government has been left struggling for solutions to the worst wave of unrest to sweep the city in 16 years as extra deployments of police and paramilitary officers appear unable to stem the troubles.

Spiraling unrest is a major source of concern in Karachi, which accounts for around a fifth of the country's GDP.

Gunmen ambushed police late on Friday, sparking gun-battles in which four officers were killed and more than 30 others wounded, officials said.

The police commandos, dressed in plain clothes, were targeted in the eastern neighborhood of Korangi, which has been immune from the troubles.

"These policemen were in a van going on a raid on a tip-off when they were intercepted by armed men who started firing, injuring many policemen," senior police official Shaukat Hussain told AFP.

"The police returned fire and at least one attacker has been killed."

"Our hospital has received 32 injured policemen, four of whom are critically injured. They all have gunshot wounds," said Seemin Jamali, spokeswoman for the Jinnah Post Graduate Medical Centre.

Karachi city police Chief Saud Mirza told AFP that four police were killed.

Witnesses in Korangi said there were pockets of intense gunfire between armed groups with ordinary people too frightened to leave home.

Speaking off the record because they were not authorised to release the information to media, two security officials confirmed that 65 people had now died in violence in Karachi since Wednesday morning.

The city's worst-affected areas are impoverished and heavily populated neighborhoods where most of the criminal gangs are believed to be hiding.

Independent economist A.B. Shahid estimated that 20 percent of the city's business was shut down on Thursday with markets closed in southern neighborhoods to protest against extortion money demanded by criminal gangs.

Underlining the brutality of the violence, one security official said bodies of those kidnapped and killed had been stuffed in sacks before being dumped in various parts of the city.

He said the bullet-riddled bodies of four young men who worked for a mobile phone company had been found in a van with their hands and feet trussed in the impoverished Shershah neighborhood.

"At least 20 killed on Thursday were kidnapped and tortured by armed gangsters. Their bodies were later stuffed in sacks and thrown away in different areas," the security official told AFP on condition of anonymity.

Notes had been left inside the pockets of clothes worn by some of the victims that read "Want more bodies?" the official said.

The independent Human Rights Commission of Pakistan said 800 people have been killed in Karachi so far this year, compared with 748 in 2010.

Copyright AFP (Agence France-Presse), 2011