Trams began their first journeys through Surry Hills to Central Station in Sydney's CBD on Tuesday night, in a significant sign of progress for the city's troubled light rail project.

Overhead lines were already energised from Central Station to Randwick, which allowed for night-time testing of the first tram – under police escort – along a much greater stretch of the 12-kilometre line. It ran through a tunnel under Anzac Parade and along Devonshire Street in Surry Hills.

A fortnight ago, trams began day-time testing to the end of the line at Randwick.

A tram undergoes day-time testing at Randwick on Tuesday. Credit:Janie Barrett

While testing of trams as far as Central Station indicates significant progress in construction over the past six months, the state's transport agency declined to say whether the line – or at least a section of it – could be opened to passengers by the end of the year.