Mayor Francis Zamora of San Juan in the Philippine capital said the gunman, who was armed with a pistol, shot one person at the V-Mall. The victim was in stable condition at a nearby hospital.

Zamora said a police negotiator was trying to talk to the gunman — a disgruntled former security guard at the shopping complex — inside a mall administration office.

"He felt bad because he was removed as a guard," Zamora told reporters, adding that the man tried but failed to convince fellow guards to join him. Aside from a pistol, the hostage taker was yelling that he had a grenade, but authorities could not immediately confirm that, Zamora said.

"We have evacuated all the people in the shopping center and we're in a lockdown here in the entire mall," he said.

An initial police report said the hostage taker, who was identified as Archie Paray, shot a mall official before rushing to the second floor of the complex, where he was holding dozens of mostly employees in an office. The report said "more or less 50 staffs" were being held hostage, but it did not provide other details.

Zamora said about 30 to 40 people were being held, adding that his estimate was based on the size of the administrative office were they were being held.

The suspect was complaining of "unequal treatment," the police report said.

He was apparently dismissed from work after abandoning his job in recent weeks without notifying management, Zamora said. He said the hostages were fine and added that authorities were trying to resolve the situation without further violence.

The gunman demanded to talk to fellow guards and the media, Zamora said, but it was not clear if officials would agree to those conditions.

More than a dozen SWAT commandos were earlier seen entering the mall, their assault rifles ready. Other policemen stood by outside, along with an ambulance.

The shopping complex, popular for its restaurants, shops, bars and a bazaar, lies near an upscale residential enclave, a golf club and the police and military headquarters in the bustling metropolis of more than 12 million people, where law and order have long been a concern.

Three years ago, a gunman stormed a mall-casino complex in Manila, shot TV monitors and set gambling tables on fire, killing 36 people who were mostly suffocated by the thick smoke. The gunman stole casino chips before he fled but was found dead in an apparent suicide in an adjacent hotel at the Resorts World Manila complex.

The attack, which caused guests and shoppers to flee to safety, was claimed by the Islamic State group, but Philippine authorities rejected the claim, saying the attacker was not a Muslim militant but a heavily indebted gambler.