Four top executives are leaving Twitter as part of an ongoing reshuffle at the US tech company, a source has told Reuters.

The firm is also bringing in a new chief marketing officer and two board members in the biggest leadership changes since co-founder Jack Dorsey returned as chief executive last year.

Those leaving include product chief Kevin Weil, media head Katie Jacobs Stanton and head of the engineering division Alex Roetter, the source familiar with the situation said.

Jason Toff, who headed Vine, Twitter's video streaming service, tweeted on Sunday that he was leaving to join Google to work on virtual reality.

Business development leader Jana Messerschmidt may also depart.

Some of the executives are leaving under pressure while others decided on their own it was time to go, the source said.

The company declined to comment, but the changes - including the names of the new executives - are expected to be announced soon.

Twitter is currently going through a rough patch: its stock has fallen nearly 50% since Dorsey's return and there are persistent concerns about its growth prospects.

Dorsey stepped in as interim CEO in July and was named as permanent CEO three months later. He was fired from his first stint as Twitter CEO in 2008.

After returning to the top job, he spoke about "hiring and investing in talent" and the need for "bold rethinking" at the social network he co-founded a decade ago.

Dorsey, also head of the mobile payments company Square, has yet to outline a detailed plan of what he wants Twitter to do differently.

But he has laid off 300 employees and brought in former Google executive Omid Kordestani.

Several executives are among those to leave the firm, but Weil, Stanton and Roetter are among the highest-level departures in recent months.

Weil has been at Twitter since 2009 and often served as the face of the company, often speaking at news conferences.

He had only been its product head for about a year in which time he developed Moments for showcasing Twitter's best tweets and content.

Twitter has been through three different product heads since 2014 and Dorsey has been playing an increasing role in product development.

Stanton, who had previously worked at Google, Yahoo and the White House, joined Twitter in 2010.

She was tasked with growing its audience outside the US. 

But Twitter had its slowest user growth last year. It now has just over 300 million users and has been eclipsed by Instagram, which passed 400 million users last year.

(Sky News)