Thirty nine people have been held as suspects.

About 500 police officers raided a building in the centre of London where they suspected drug trafficking was taking place.

Streets around the four-storey block, in Charing Cross Road, were sealed off and traffic in the area came to a standstill.

Some of the officers were believed to be armed and had search warrants under the Misuse of Drugs Act as well as the Firearms Act.

Well-planned operation

Chief Superintendent Jim Overton, from Holborn Police Station, said the premises, in a block in Denmark Place, were still being searched by officers while suspects were in custody.

"This has been running for months," Mr Overton said.

"Rather than just go for the people in there, we are going for the organisers."

He said substances recovered in the raid still had to be analysed but added: "We are very pleased with the results so far. It looks very, very promising."

The raid cause major disruption to rush-hour traffic.

Dozens of onlookers gathered at police barricades across Charing Cross Road attempting to get a glimpse of the police operation.

Police later re-opened Charing Cross Road but officers kept Denmark Place itself sealed off.