Drugs worth £2m vanish from force's famous HQ at 36 Quai des Orfèvres, just months after building was mired in rape allegation

Paris police are investigating the disappearance of 51kg of cocaine from a supposedly locked and sealed room in their own headquarters on the banks of the Seine.

The cocaine "bricks" with a street value of around €2.5m (£2m) were seized a month ago after officers smashed a drug trafficking network in the capital.

They were supposed to be under lock and key at the force's legendary headquarters at 36 Quai des Orfèvres, for ever associated with the fictional French detective Maigret.

Officials say the cocaine, placed in numbered evidence bags, was definitely still in the secured store room on 23 July when it was last checked, but was definitely missing on Thursday.

Police chiefs immediately ordered an inquiry, and the force's own internal investigations squad was sent into the building with sniffer dogs. So far, there have been no leads.

It is the second time this year that 36 Quai des Orfèvres has made damaging headlines.

In April, two officers belonging to an "anti-gang crime" squad were put under official investigation for the alleged rape of a 34-year-old Canadian woman visiting Paris. She had met the men during an evening of heavy drinking at a nearby Irish pub. The officers said she agreed to follow them to their headquarters, just across the Seine from the pub. Once there she said she was raped. One of the police officers charged admitted having sex with the woman, but claimed she had consented. The investigation is ongoing.

Interior minister Bernard Cazeneuve has ordered the national police investigation squad to leave no stone unturned in its search for the missing drugs and promised the culprits would be treated with "the utmost severity".

In a statement, the prefecture of police said: "This investigation will look into whether the relevant rules were followed for the management of evidence in the offices of this brigade in particular, and at 36 Quai des Orfèvres in general."

It promised "very firm measures" would be immediately taken "if the investigation shows the law has been broken".