The prison guards keep a close watch on the convicts.

狱警密切监视囚犯。

The State Flood Control and Drought Relief Headquarters issued a warning urging provinces to keep a close watch on the changing weather and act to avert possible danger.

国家防汛抗旱总指挥部发出预警，要求各省密切关注天气变化并采取行动避免潜在危险的发生。