Occupy Boston protesters are facing eviction after the city's mayor gave them a deadline of midnight to leave their encampment.

Demonstrators have been camped at Dewey Square since late September, but on Wednesday lost a bid to legally remain in the space.

Mayor Tom Menino has previously been sympathetic to the occupation, but issued the midnight ultimatum on Thursday morning. Occupy Boston swiftly responded by calling for people to gather at their camp tonight to try to prevent an eviction.

The Boston Globe reported that Menino made the comments before a news conference this morning.

"If not, we'll take further action," the Globe quoted Menino as saying.

A spokeswoman for Menino told the Guardian the deadline of midnight Wednesday was accurate. She was unable to elaborate on whether protesters would be forceably evicted.

Occupy Boston had previously been granted a restraining order which prevented Boston police from evicting the protest from Dewey Square, however this was overturned yesterday. At the same court hearing the group's motion for a preliminary injunction, which would also protect them from eviction, was rejected.

On Wednesday night Menino said following the decision "the city will act appropriately to fulfill our duty to preserve the public's peace and safety."

The @Occupy_Boston Twitter feed was swift to respond to Menino's ultimatum, posting: "If you support #occupyboston please come to camp tonight and help defend the 1st amendment and the 99%."

Before this week Menino had said he had no plans to evict protesters, but on Tuesday he appeared to be losing patience with the city's occupation, telling reporters the group were "aiming their fire at the wrong place".

"Mayors can't do much about what they're talking about. It's the Congress and the Senate but nobody's talking to them at all. They come at mayors," the Boston Herald quoted Menino as saying.