KARACHI (AFP) - Schools and businesses went on strike in Pakistan's financial capital Karachi on Friday as the country's top court accused the government of failing to prevent record levels of unrest.

Security and human rights officials estimate that around 300 people have died in the city of 18 million since January 1, many of them as a result of political, ethnic and sectarian tensions plaguing the country's business hub.

Security officials confirmed six more deaths overnight, bringing to 16 the toll from shootings and a bombing in the last 36 hours.

The unrest comes with general elections due by mid-May. The polls are due to mark the first democratic transition of power in Pakistani history.

"Karachi is burning, people are being violently killed everyday yet the authorities are doing nothing to save innocent people's lives," said Supreme Court judge Jawwad Khawaja at a hearing to review the violence on Friday.

"People have lost confidence in the police, witnesses in murder cases are being killed and even policemen are not safe who are being murdered in line of duty," said fellow judge Khilji Arif Hussain.

On Friday, most markets and shops were closed after several religious parties called for a strike to protest against the January 31 killing in Karachi of Abdul Majeed Deenpuri, a top cleric at one of Pakistan's largest seminaries.

Schools were closed, traffic was thin and attendance in offices was below normal, an AFP reporter said.

Ethnic, sectarian and politically-linked violence in Karachi killed at least 2,284 people in 2012 in the deadliest such violence for two decades, according to the independent Human Rights Commission of Pakistan.