An ex-policeman armed with a high-powered assault rifle hijacked a bus carrying more than 20 Hong Kong tourists including children in the Philippine capital on Monday, police said.
Six hostages, three of them children, were released by the gunman about three hours after the standoff began, with the drama being played out live on national television.
"There are children and adults on the bus," Metro Manila police commander Director Leocadio Santiago said on DZBB radio. "He is armed with an M-16 assault rifle," he added.
Police said they were negotiating with the gunman, a former policeman who was discharged in 2008 for his alleged involvement in drug-related crimes and extortion, and was demanding to be reinstated.
Children could be seen peeking from the drawn curtains as a lone police negotiator stood near the scene at a popular tourist park in Manila.
A national police statement said at least 22 tourists from Hong Kong were on board the bus, along with the driver. Earlier, police had said they were South Koreans.
"We have never had anything like this before -- we are very much concerned," said Joseph Tung, executive director of the Travel Industry Council of Hong Kong. "We hope the tour members will be released as soon as possible."
He said there had been 20 passengers on the bus, aged four to 72, plus a Hong Kong escort and local guide leading the three-day tour, when it was seized. The tour group was scheduled to return to Hong Kong late Monday.
Tung said the council, which represents Hong Kong's travel sector, had not been told of any ransom demands for the hostages' release.
"We have heard nothing like that so far," he said.
Hong Thai travel agency, which ran the tour, could not be immediately reached for comment.
About three hours after the stand-off began, the ex-policeman released six people.
Live television footage showed the bus parked in front of a grandstand at Rizal Park, a popular tourist destination just a few blocks from the police headquarters.
Santiago identified the suspect as Rolando Mendoza, a decorated former police senior inspector before he was accused and relieved of his post.
National police spokesman Senior Superintendent Agrimero Cruz said the bus had been isolated and police had deployed commandos in the area, adding that talks with the gunman had begun.
"Negotiations are ongoing," Cruz told reporters.
The hostage-taking came hours after a South Korean man was killed in a separate attack on a vehicle by gunmen elsewhere in Manila. Two of his companions were seized at gunpoint but later released.
The motive for the attack was not clear, although kidnap-for-ransom gangs often target foreign tourists and businessmen in areas near Manila and in the provinces.
Police said the incidents were not related.
Monday's bus hijack recalled a similar hostage-taking in 2007, when a troubled civil engineer armed with a grenade took over a bus and held 30 children but freed them after a 10-hour standoff with police.