NEW YORK • A surprise new album by Kendrick Lamar opened on Sunday at No. 1 on the United States chart in the latest triumph for the critically acclaimed rapper. The album - the fourth by him and titled untitled unmastered. - sold 178,000 copies or the equivalent in streaming in the US in the week through last Thursday, Nielsen Music said.

Lamar, 28, released untitled unmastered. without notice on March 4 in the wake of the Grammys, where he was the music industry gala's biggest winner with five awards.

He characterised the album as a series of rough works from the studio, although the songs take on heavy themes including an opening track that mixes images of the biblical apocalypse and contemporary social ills.

He also went to No. 1 last year with To Pimp A Butterfly, a reflective look at the state of black America that experimented with jazz elements, which are also apparent on untitled unmastered.

The latest album scored despite the lack of a physical release. A CD came out last Friday, seven days after the digital version and too late to be considered for the first- week chart.

Discrepancies between digital and physical release dates, which once enraged record stores, have become increasingly commonplace as the popularity of streaming transforms the music industry. Rap superstar Kanye West has said he has no plans to release a physical version of his latest work, The Life Of Pablo, and vowed to stream three new albums a year.

AGENCE FRANCE-PRESSE