Detectives investigating the disappearance of the chef Claudia Lawrence were last night searching an area close to York University after receiving "new information".
Police said the operation in the Heslington area, close to where Ms Lawrence worked, was the result of information received "in the last few days". Ms Lawrence, 36, was last seen on the afternoon of 18 March last year.
Officers are now treating her disappearance as a murder inquiry. North Yorkshire Police said: "Police investigating the disappearance of Claudia Lawrence are conducting searches in an area of York known as the Outgang which is in the Heslington area. The searches, which began on Tuesday, are expected to take up to three days."
Ten officers and three police dogs have been involved in the search so far. A spokesman added that the search was not related to an appeal issued last week about Ms Lawrence's whereabouts on the evening of 16 March last year, when she was said to have spent the night with a mystery man.
The day before she was last seen, the university chef told a friend by text message that she had been out with the man until at least 4.30am.
The Claudia Lawrence investigation is one of the largest ever carried out by North Yorkshire Police and has so far cost more than £600,000.
On the eve of the first anniversary of her disappearance, it also emerged she had been having an affair for several months with a man who had a long-term partner at the time she vanished. Police urged anyone with information about these two men to come forward to assist their inquiry.
Ms Lawrence failed to arrive for work on 19 March 2009. Police believe she may have come to harm by someone she knew.