HONG KONG - Tens of thousands of Hong Kong people are expected at a weekend rally to demand justice for the victims of this week's hostage bloodbath Manila, organizers said Friday.

In a rare show of unity, Hong Kong's pro-Beijing and opposition groups will jointly hold the march on Sunday to express anger and grief at the Philippine government's handling of the crisis, in which eight Hong Kong tourists were slain.

"We will take to the street to mourn the victims on Sunday," Cheung Man-kwong, Democratic Party lawmaker and one of the conveners of the rally, told Agence France-Presse.

"We will also demand that the Philippine authorities conduct a fair and independent investigation on the incident and have representatives from the Hong Kong government take part."

The office of the pro-Beijing Democratic Alliance for the Betterment and Progress of Hong Kong (DAB) confirmed that it will take part in Sunday's rally.

All other political parties in the city's legislature had agreed to join the march, which will start from Victoria Park at 3pm Sunday (0700 GMT), Cheung said.

Cheung said findings of the investigations being conducted by the Philippines would not convince Hong Kong people because it would rely only on the statements of their police.

"None of the survivors has been asked to give an account of the event. The investigation report is bound to be one-sided and unconvincing," Cheung said.

Armed ex-policeman Rolando Mendoza hijacked a busload of Hong Kong tourists in Manila on Monday as part of a bid to get his job back and have himself cleared of extortion charges.

Eight of the tourists and the gunman were killed in the final stages of the 12-hour ordeal, when ill-equipped and poorly trained police launched an assault on the bus as the events were broadcast around the world live on television.

Questions were raised over whether the victims were killed by bullets fired by the hostage-taker or police during the bungled rescue operation.

A national police spokesman for the Philippines said Friday initial findings from their investigation showed that the bullets that killed the tourists likely all came from Mendoza and not from the police rescue team.

Hong Kong government said Thursday that the city's coroner had ordered autopsies for all eight victims, which may lead to an official inquiry by the Hong Kong Coroner's Court into the bloody standoff.

But critics said the court did not have the authority to compel the Philippine police to testify or hold them accountable for their mistakes.

"The most the court can do is to come to a conclusion that throws doubt on the Philippine authorities' findings," Cheung said.