HONG KONG - A shell-shocked Hong Kong clamored for answers from Philippine authorities Tuesday as flags flew at half-mast in memory of 8 tourists killed in a bloody hostage drama in Manila.

The Hong Kong government raised a "black" travel alert for the Philippines, urging against all travel to one of Southeast Asia's most popular tourist spots. Tour groups said they were canceling all organized visits.

Flags on Hong Kong government buildings flew at half-mast as a mark of respect for the victims of Monday's day-long bus siege in Manila, which played out live on global TV, and the stock exchange was holding a minute's silence.

Lurid photographs of the chaotic climax dominated the front pages of the Hong Kong press, with editorials echoing the Chinese territory's leader in querying the response of Philippine authorities.

"The way it is handled -- particularly the outcome -- is very disappointing," Hong Kong Chief Executive Donald Tsang told reporters late Monday.

The Chinese embassy in Manila on Tuesday "urged the Philippine side to take concrete measures to ensure the safety and security of the Chinese citizens in the Philippines."

The 8 Hong Kong tourists, who were part of a tour group, were killed when police stormed a bus that had been commandeered 12 hours earlier by a disgraced ex-police officer demanding his job back.

"There were so many people on the bus -- no one came to our rescue. Why?" one Hong Kong survivor, who identified herself as Mrs Leung, said at the scene.

"We were in fear for so many hours. I find it really cruel."

Hong Kong media said Mrs Leung's husband had died in a hail of bullets as he tried to protect his wife. The couple's three children aged 14, 18 and 21 were also on the bus and remained unaccounted for, according to the reports.

The government organized two chartered flights by Hong Kong's flag carrier Cathay Pacific to take relatives of the hostages, as well as psychologists, doctors and social workers, to Manila.

While Manila police defended their actions, the Hong Kong leader complained that he had been unable all Monday to reach Philippine President Benigno Aquino, and urged authorities to give a full account of the crisis.

The crisis began when the suspect, armed with an M-16 assault rifle and dressed in combat pants, hijacked the bus with 25 people aboard in Manila's tourist district. He later freed seven Hong Kong tourists and two Filipinos.

Negotiations broke down after nightfall when the gunman, former senior police inspector Rolando Mendoza, began shooting and commandos stormed the bus, firing dozens of bullets of their own into the vehicle.

Chinese Foreign Minister Yang Jiechi telephoned his Philippine counterpart to express Beijing's shock and demand a thorough investigation, the official Xinhua news agency said.

"We strongly request the Philippine and Chinese governments to investigate and give satisfactory answers to the Hong Kong people," the Apple Daily said.

Noting the length of time it took Manila police to intervene, the newspaper said in an editorial: "It makes people question the competence of the police."