By Imtiaz Shah

KARACHI, Pakistan (Reuters) - A bomb exploded in a crowded area of Pakistan's southern port city of Karachi on Tuesday, killing at least one person and wounding 21, police said.

Two of the injured were in a critical condition, police spokesman Imran Shaukat said.

It was not immediately clear what was the target of the blast in the Aisha Manzil area of Karachi. The explosion was heard several kilometers (miles) away.

Karachi is home to 18 million people and is the financial capital of Pakistan.

Authorities there have been unable to clamp down on militancy and violent crime. Between five and 10 people are murdered there every day, but bombings are less common.

Pakistan, a nuclear-armed country of 180 million people, is plagued by a Taliban insurgency, daily power cuts and endemic corruption.

(Reporting By Katharine Houreld)