The elusive artist Banksy has confirmed he painted swimming piranhas on to a City of London Police sentry box, which was first spotted on Sunday morning.
The glass-fronted box on Ludgate Hill - near The Old Bailey and St Paul's Cathedral - has been transformed to look like an aquarium.
This is his seventh new artwork to be revealed in the capital in as many days, following a goat, monkeys, elephants, a wolf, pelicans and a cat.
Crowds gathered to take photos throughout the day until barriers were installed, preventing people from going inside.
This work differs from the previous works by Banksy unveiled this week in that it is a detailed painting that appears to have been created with translucent spray paint.
The City of London Police said it was aware of "criminal damage" to the police box and were liaising with City of London Corporation which owns it.
A corporation worker was earlier seen barricading it off and asking spectators not to stand in the road near it.
A spokesperson said: "We are currently working through options to preserve the artwork."
The sentry box is among many installed in the 1990s used by police officers monitoring traffic to prevent IRA attacks.
'Really uplifting'
A local resident who came to take pictures of the fish artwork said she thought it was "rather beautiful in the sun."
"I like it, it's got a charm to it somehow. It's not in your face, it's quite subtle.
Artist Daniel Lloyd-Morgan, who has painted most of Banksy's new pieces of art this week said: "It's really uplifting for people in London at the moment.
"There's a buzz around his work. It's nice to capture that as I do the people as well.
"It's not just about the artwork, it's about the whole environment he's creating, it becomes a sort of work of art itself - what happens to it, people steal it or take it away."
Mr Lloyd-Morgan added that he was due to go on holiday on Monday but has postponed it in case Banksy's art revelations continue next week.
Banksy's week-long London art trail
Banksy's translucent fish swimming around a 1990s police sentry box form the seventh piece in a surprise animal-themed art series.
On Monday, a goat appeared on the side of a building near Kew Bridge, followed by a sweet image of two elephants touching trunks on the side of a house in Chelsea on Tuesday.
Three monkeys hanging from a bridge in Brick Lane then drew crowds on Wednesday.
On Thursday, a howling wolf on a satellite dish - which looked like the wolf was howling at the moon - was installed onto a garage roof in Peckham.
On Friday, locals in Walthamstow woke up to find two pelicans fishing above a fish shop.
And on Saturday, a stencil of a cat having a stretch appeared on an empty billboard in Cricklewood.
In total, three of these works have since been removed or defaced.
The billboard, along with the cat, was taken down by contractors citing safety reasons, hours after it was revealed.
Crowds who had gathered to look at the work booed as it was dismantled by three men.
The affectionate elephants were pictured having been painted over with stripes on Friday. And earlier in the week, the satellite dish and its wolf were apparently stolen by masked men within hours of being revealed.
Each day, the artist officially announced the works on his Instagram page.
