A policeman was killed and another injured.
Rumors of more explosions swept the city.
Police emptied a shopping mall in Makati after they discovered an abandoned package but later found that it contained only mangoes, mushrooms and underwear.
Presidential spokesman Mike Toledo denied the bombings were an attempt to impose martial law.
"There are some people, and I understand it's some members of the opposition, who have already taken advantage of this situation by blaming the administration ... that somehow these are a prelude to martial law," he said.
A statement from a coalition of opposition parties said it was feared "these attacks are coming from people who fear the truth that is coming out at the impeachment trial."
"We warn Malacanang [the presidential palace] not to allow these terrorist attacks as an opportunity to create conditions of martial law or a state of emergency."
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