STOCKHOLM (AFP) - Swedish police said on Tuesday that they were still trying to find out why the car of British indie band Viola Beach broke through two barriers and plunged off a canal bridge this weekend, killing the musicians and their manager.

"We have not found anything that could explain what happened. We do not know," police spokesman Lars Bystrom told AFP.

Early Saturday, the car, which one witness said was travelling at around 70kmh, drove through several signal lights and two barriers towards a canal bridge near Stockholm - the centre of which was up to let a vessel pass.

The four band members and their manager, aged between 20 and 35, died when the car crashed 26m into the water.

Lorry driver Jonny Alexandersson told the Aftonbladet newspaper that other vehicles were waiting for the bridge to close fully, but the band's car sped towards the bridge "at a crazy speed".

Swedish police and bridge operators said that the barriers and signal lights were working normally at the time of the crash.

"For the moment we are examining the car, to see if everything functioned properly, including the brakes, and we are examining the bodies of the people that were inside," Bystrom said.

When asked what kind of tests police were conducting, Bystrom said authorities were carrying out "routine tests for this kind of accident".

Swedish public broadcaster SVT reported that the crew of the vessel for which the bridge had been lifted said they saw something fall into the water but were given the green light.

Police told AFP they were looking into the claims.

The band, who last year released a debut single, had been in Sweden for a Friday night "Where's the music" festival in the central city of Norrkoping and were headed back to Britain for a gig the following day.