A search was launched after a child was heard crying out near a rubbish tip.
A worker at the community dump off Wilson Avenue, Brighton, heard a youngster calling "No, no, no" and raised the alarm at 4pm yesterday.
Police and firefighters, using heat-seeking equipment, scoured the area west of the tip for more than three hours but nothing was found.
Bad weather prevented the Sussex Police helicopter from joining in but it was expected to help when the search resumed this morning.
A second search was launched at 2.20am today after a man dialled 999 saying a man had been stabbed near Duke's Mound, Brighton.
Nothing was found but police planned to search again today.
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