Guests and staff were evacuated from a five-star Knightsbridge hotel as 120 firefighters tackled a large fire on the roof.

London Fire Brigade said 20 engines and 120 firefighters and officers had been sent to the scene at the Mandarin Oriental Hyde Park, in Knightsbridge, as huge plumes of thick black smoke could be seen rising into the sky.

Emergency services, including fire engines and ambulance vehicles, were still arriving at around 4.45pm, almost an hour after the fire brigade was first called at 3.55pm.

Flames could be seen around the top of the hotel, and extended ladders were erected to access that area of the building.

Emergency services outside the Mandarin Oriental hotel in Knightsbridge

The 12-storey five-star hotel completed the "most extensive restoration in its 115-year history", according to a statement published by owner Mandarin Oriental Hotel Group in May.

All 181 bedrooms and suites are "now more luxurious and comfortable than ever before" and the building's "iconic facade was revitalised", the company said.

The hotel is located between Hyde Park and the Knightsbridge shopping district, which includes Harrods.

A tradesman working at the hotel said he saw a "big fire" on the roof before raising the alarm.

The 19-year-old lift engineer, who gave his name as Harry, said: "I said (to my colleague) 'Lee, there's a fire over there, let's get out of the building. Get out the lift shaft, I'm being serious'.

"We ran down the stairs and went and got the scaffolder out of the loading bay."

He said the builders on the roof had been cutting materials and doing other work during the day.

"I could see the orange flames on the roof," he said.

Staff from the hotel have been evacuated to Hyde Park where they were being given bottles of water.

One worker, who asked not to be named, said: "The fire alarm started and everybody was told to get outside.

"Everything's fine but we don't know how it started yet."

Jack Martin, a 21-year-old student from Peckham, said he was coming out of Knightsbridge station when he saw a "huge billow of smoke".

He told the Press Association: "I obviously was quite shocked when I saw all that smoke.

"But they were evacuating the building when I arrived, there were a fair amount of staff and guests and it was all fairly orderly.

"It was all quite calm and collected, there wasn't any hysteria and I thought it was well organised."

Emergency services had since cordoned off the road, he said, and although there were ambulances present he had not seen any signs of injury.

"I would say the fire is under control now. I can't see any smoke, there are firefighters and the whole building is dripping wet right now," he added.

Another witness, Samir Boureghda, of Masgouf restaurant in William Street, said he thought the flames had been extinguished.

He added: "There's no more fire, it was really too much.

"The fire was in the middle of the hotel.

"There was a lot of smoke, black smoke.

"It was a big fire."

Smoke seen billowing from the Knightsbridge hotel

Eyewitnesses posted videos on social media showing the large column of smoke rising from the top of the building and people in nearby Hyde Park turning their heads towards the sky.

One user called Arthur said: "Looks really bad. Prayers to those inside."

An LFB statement said: "The hotel has been evacuated by hotel staff and crews are currently working to bring the fire under control as well as carrying out a systematic search of the building.

"Firefighters are likely to be on the scene throughout the night.

"The cause of the fire is not known at this stage."

Transport for London said the Sloane Street entrance of the Knightsbridge Tube station had been closed due to the fire and customers were advised to leave by Harrods.

London Ambulance Service and Metropolitan Police are also attending the scene.