Mourners have started paying their final respects to six worshippers gunned down by a white supremacist at a Sikh temple in the US almost a week ago.

A day after members were allowed back into the Sikh Temple of Wisconsin for the first time since Sunday's attack, the country's top lawyer, US Attorney General Eric Holder, and Wisconsin Governor Scott Walker were scheduled to speak.

Then, a series of priests will read the Sikh holy book from cover to cover in a rite honouring the dead called "Akhand Path". It takes 48 hours.

"We want to pay homage to the spirits who are still in there," said Harpreet Singh, a nephew of one of the victims.

Hundreds of mourners, many of them Indian-American, milled through a school gymnasium to the sound of chanting as images of the victims were projected on a large screen.

Federal investigators might never know for certain why 40-year-old Wade Michael Page chose to attack strangers. The Army veteran opened fire with a 9mm pistol, killing five men and one woman, and injuring two other men.

The dead included Satwant Singh Kaleka, 65, the temple president, who was shot as he tried to fend off Page with a butter knife.

Authorities say he ambushed the first police officer who responded, shooting him nine times. A second officer shot Page in the stomach and Page killed himself with a shot to the head.

The officer who was injured, Oak Creek Police Lieutenant Brian Murphy, is in a "satisfactory" condition.

The others killed were Ranjit Singh, 49, and his 41-year-old brother Sita Singh; Suveg Singh Khattra, 84, Prakash Singh, 39, and Paramjit Kaur, 41.

The FBI roped off the temple for four days while agents conducted their investigation. They handed the keys back to Sikh leaders on Thursday morning.

Workers then spent the day cleaning up, repairing bullet damage, shampooing carpets and repainting walls to rid the temple of traces of the carnage.