New CCTV footage exclusively obtained by BBC News reveals how a burglar stole more than £10m worth of jewellery and designer handbags from a London mansion.

The images show a masked man stuffing handfuls of jewellery into a backpack after creeping into the multi-million-pound property.

A family spokesperson, who was inside the home when the theft was carried out, said the intruder moved "like a cat" but appears to have almost been thwarted when his apparent escape route was blocked.

The stolen goods belong to Hong Kong socialite Shafira Huang, who was not at the St John's Wood house at the time, and a reward of up to £1.5m has been offered as the hunt for the thief continues.

Csaba Virag, a spokesman for Ms Huang's family, said the thief had initially attempted to enter via a second-floor window at around 17:00 GMT on 7 December.

Marks that look like they were made with a screwdriver or crowbar were left behind.

When that did not work, the intruder then climbed onto the roof, where he would have seen two housekeepers leaving the grounds, before lowering himself into a large concrete gutter to enter the house via a bathroom window which was also on the second storey.

The bathroom belonged to a live-in governess, Mr Virag said, who he was holding a meeting with in a basement room of the five-storey property when the theft occurred.

"She would have been in that room and there would have been a confrontation, which is quite scary," he said.

Mr Virag said the intruder would have had to climb down onto a sink from the window, but moved "like a cat" to avoid making any marks on it or disturbing the cosmetic products it was littered with. Around £300 in cash on a desk in the room was left untouched.

The family spokesman said he heard a banging during that meeting but put it down to the strong winds outside.

"Retrospectively, I can put two and two together, which at the time you don't really think," he said.

Mr Virag said he believes the noise could have been a staff entrance door banging in the draft created when the intruder opened the window, and that the thief closed the window quickly to avoid being given away.

The intruder was then captured on CCTV cameras moving around the house above them, struggling to open cases containing expensive jewellery before putting items into his bag.

Time stamps on one CCTV image released by the family indicate he narrowly avoided bumping into the maid when they walked through the same hallway seconds apart.

Asked if the thief left the house the same way as he came in, Mr Virag said he did, but added "I believe it was not his intention".

The thief had entered a "high risk" part of the house and appears to have tried to leave via a rarely used guest room at the back of the property, Mr Virag said.

He continued: "[He] tried to open the window from the inside but we have the safety on the sash window.

"The stoppers only allow you to pull it down 8cm and if you don't have the right tool to unscrew the pins, you can't. He tried but couldn't succeed."

As well as jewellery, Hermes Crocodile Kelly handbags and £15,000 in cash were also taken.

The thief, who police believe may have been armed, is believed to be a white man in his late 20s to 30s.

"We urge anyone who was in the area of Avenue Road, NW8, and saw anything suspicious to please come forward," the Metropolitan Police's Det Con Paulo Roberts said.

"Also, if you have seen this jewellery since, someone has offered to sell you it, or you have any further information, then please also contact the police or Crimestoppers anonymously."

A £500,000 reward has been offered for information that leads to the arrest and conviction of the suspect.

A second reward of 10% of the value of any recovered items has been offered by the homeowners for information that leads to the retrieval of the stolen jewellery - which could total as much as £1.5m, the Metropolitan Police confirmed.

The burglary was carried out on Avenue Road, which links the Swiss Cottage and Regent's Park areas of the capital and is home to some of the city's most expensive properties.

Ms Huang, who lives in the mansion with her property developer husband, had been a prolific social media user but has since made her profiles private.