Former Maryland governor Martin O'Malley. (AP Photo/Bruce Smith, File)

DURHAM, N.H. -- Former Maryland governor Martin O'Malley, who has been ramping up for a potential White House bid, plans to make an announcement about his political future on May 30 in Baltimore, aides said Wednesday.

O'Malley, who is widely expected to run for the Democratic nomination, will tell donors and other supporters about the announcement in a conference call scheduled for Thursday night, according to aides who requested anonymity in order to speak more freely.

The aides expect O'Malley to say he is inclined to run but to remain somewhat circumspect about his intentions. Were he to tell them outright that he plans to enter the race, he could trigger a 15-day window that would require him to file candidacy papers before May 30.

An email alerting O'Malley supporters to Thursday night's call promised "an important update on his imminent 2016 plans." People familiar with the planning said several locations within Baltimore have been under consideration for the May 30 event.

[The Fix: O'Malley is getting bolder and bolder, and that's a problem for Hillary Clinton]

The announcement of an apparent announcement date comes amid several other activities that strongly suggest O’Malley is moving forward with a longshot bid for the Democratic nomination that would pit him against overwhelming favorite Hillary Rodham Clinton. Vermont Sen. Bernie Sanders (I-Vt.) has also entered the primary race, and former Rhode Island governor and senator Lincoln Chafee and former Virginia Sen. James Webb are considering it.

O'Malley spent Wednesday in New Hampshire, the nation's first presidential primary state. He looked very much like a candidate during stops at a diner in Manchester and a house party here. The house party drew about 50 people, many of whom were seeing O’Malley for the first time.

At several points, O'Malley, who is trying to position himself as a more progressive, forward-looking alternative to Clinton, told reporters and party activists that they could expect a decision about his plans "very, very shortly."

“I believe that there’s plenty of room for a more open conversation,” he said when asked about the contest for the Democratic nomination.

O’Malley’s choice of Baltimore as the location for his May 30 announcement is not without risk, especially given recent demonstrations and unrest linked to the arrest and death of 25-year-old Freddie Gray. O’Malley, who spent seven years as Baltimore's mayor, has faced renewed criticism of his “zero tolerance” policing policies since the death of Gray, who was severely injured while in police custody.

As he visited New Hampshire on Wednesday, O’Malley defended his policies, which were credited for reducing violent crime, and said the country needs to invest more heavily in its cities, which he said policymakers from both parties have neglected for years.

O’Malley was trailed Wednesday by media consultant Jimmy Siegel and his camera crew. Siegel, who did work for Clinton’s presidential campaign in the 2008 cycle, previously produced a campaign-style video for O’Malley that has been used to introduce him to Democratic audiences around the country. Siegel would not say whether he will have a formal role with O’Malley going forward.

Other recent O’Malley activities are also consistent with a coming campaign launch. On Monday, he gathered in New York with about 30 progressive activists, academics and MSNBC contributors and hosts.

On Tuesday, close to 50 supporters and friends met with O’Malley at the Baltimore-area home of a long-time backer, according to aides. Attendees included several former staffers from his time as Maryland governor and Baltimore mayor.

Former Maryland governor Martin O'Malley attended a fundraiser for the Merrimack County Democrats at a bookstore in Concord, N.H. (Twitter/Liisa Rajala, New Hampshire Business Review)

In coming days, aides said, O’Malley is also planning to attend get-togethers in Montgomery and Prince George’s counties, which border Washington and are Maryland’s two largest Democratic jurisdictions. Aides said Montgomery County Executive Isiah Leggett (D) is hosting the Montgomery event, while Yvette Lewis, a former Maryland Democratic Party chairwoman, will host the Prince George’s gathering.

Aides said that O’Malley’s political action committee has also been staffing up in recent weeks. Last week, the PAC announced the hiring of Karine Jean-Pierre, a former aide to President Obama, as O’Malley’s national political director. O’Malley has also added two more members to his press staff.