Customers around the world who pre-ordered Samsung's Galaxy S4 handset so they could have one on the day it is released face delays of up to a week.
UK operators were today forced to send messages to customers after Samsung blamed 'unprecedented demand' for the Android handset.
US customers were also being warned of delays.
The Galaxy S4 goes on sale around the world this weekend - but Samsung has admitted it has not been able to keep up with demand, leaving customers who ordered weeks ago facing delays
Customers around the world who pre-ordered Samsung's Galaxy S4 handset so they could have one on the day it is released face delays of up to a week, the firm revealed today
The firm told MailOnline it was unable to meet demand in the UK - even though customers had ordered weeks ago.
'There has been unprecedented demand for the Galaxy S4 in the UK,' the firm said.
'Samsung is working hard to ensure that pre-orders and sales across all channels are fulfilled as soon as possible.'
More...
Growing old on Facebook: Search data reveals we talk more about the weather and politics as we age
Interplanetary impacts: Nasa captures astonishing moment meteors smash into Saturn's rings
Samsung unveiled the Galaxy S4 in a glitzy New York event in mid-March and planned the worldwide launch for 27 April.
Many thousands are believed to have pre-ordered the phone so it would arrive on launch day may now get their handset later.
The firm has undertaken a big budget 'world tour' to launch the handset. Here, a photograph is projected onto the sails of the Opera House as Samsung Electronics Australia transformed the iconic sails of the Opera House into a visual display showcasing hundreds of photographs submitted by ordinary Australians on Facebook
UK operator 3 told the BBC that Samsung was 'experiencing stock constraints' and said it regretted the frustration this would cause customers.
The UK's other major operators also said they were having stock problems but were looking to prioritise customers who pre-ordered over those that walk into shops to buy the gadget.
Similar delays were being reported in the US with operator Sprint delaying the opening of its online S4 store by a week to cope with demand.
Experts expect the handset to be a smash hit.
'I believe the Samsung Galaxy S4 could be an important milestone for the Korean company, as it could be the first smartphone to outsell an iPhone,' said Francisco Jeronimo, an analyst with IDC.
'The Samsung Galaxy S4 can be a game changer for Samsung, and I believe for the first time that this device has the potential to outsell the next generation of iPhone - assuming that Apple will incrementally improve the next version of the iPhone.'
The highly anticipated Samsung Galaxy S4 goes on sale in the UK tomorrow - but the firm has warned customers, even those who pre-ordered, that they may face delays because of demand
It comes as Samsung revealed strong smartphone sales have driven its income up 42 per cent to a record high despite a typically slow season for the electronics market.
The world's largest smartphone maker said its first quarter net income reached 7.2 trillion won (£4.2billion) in the first three months of 2013, compared with 5 trillion won a year earlier.
The figure was a surprising two per cent increase from the previous quarter. Analysts expected Samsung to report lower profit than the fourth quarter because demand typically slows.
But sales of Samsung's flagship smartphone, the Galaxy S III, and the oversized handset device called the Galaxy Note remained strong and shored up profit, Samsung said.
SAMSUNG GALAXY S4 - WHAT THE CRITICS SAY
AllThingsD: 'Galaxy S 4 Is a Good, but Not a Great, Step Up'
'If you’re a nut for lists of new features, love Samsung or crave an even bigger display, the Galaxy S 4 may be for you. It’s a good phone, just not a great one.'
T3: 'A Real Beauty' (5/5)
'It feels good, looks smart and does more than previous smartphones have. On the other hand, just as most people only scratch the surface of the capabilities of their home computers, settling for email, word processing and a little light gaming, there are going to be a lot of customers who barely dig into the features here.'
The Verge: Great To Use, Unpleasant To Hold (4/5)
'I don't like holding this phone, and I can't overstate how much that informs the experience of using it. It makes an awful first impression, slippery and slimy and simply unpleasant in your hand.'
Engadget: 'Predictable Excellence'
'If you're considering a move from an older Samsung device, the GS 4 is absolutely the handset you want.'
Techcrunch: 'The S Stands For Super, Not Simple'
'It’d be foolish to think that the Galaxy S4 isn’t a top-notch phone. But in playing with this phone for a while, adjusting to the new features, trying to make the most of them, and sometimes failing miserably, I keep returning to the idea of 'Keep it simple, stupid.'
It also spent less on marketing its mobile devices than it did in the previous quarter when competition heated up with rivals.
Sales rose 17 per cent to 52.9 trillion won.
Operating profit was up 54 per cent to 8.8 trillion won, in line with its preliminary results released earlier this month.
Analysts expect Samsung to report another record-high profit during the April-June quarter as the Galaxy S4, the latest iteration of the Galaxy S smartphone, goes on sales worldwide, months before Apple introduces a new version of the iPhone.
Samsung said initial orders for the Galaxy S4 were higher than expected, making it difficult to meet demand. Lee Don-Joo, head of sales and marketing at Samsung's mobile division, said sales of the S4 will be higher than its predecessor.
A tale of two smartphones
SAMSUNG GALAXY S4
Height: 136.6 mm (5.38 inches)
Width: 69 mm (2.72 inches)
Depth: 7.9 mm (0.31 inches)
Weight: 130 grams (4.59 ounces)
Touchscreen: 5in
Pixel density: 441 per inch
Display: 1920-by-1080 pixels
Network speeds: 3G and 4G LTE Lite
Camera: 13 megapixel in back-facing camera, 2 megapixel in front-facing
Voice recognition: Can translate nine languages and utilizes voice-activated tools that can dictate, reply, forward or save text messages
Built-in apps: Video chat; internet browser; Gmail; Google Talk, Google Play Store; infrared LED; Google Maps; YouTube
Processor: 1.9GHz quad-core processor or 1.6GHz octa-core processor
Internal memory: 16GB; 32GB; or 64GB
Other memory: Data stored in Samsung's HomeSync - a household cloud service
Battery: 2,600 mAh
Operating system: Android 4.2.2 Jelly Bean
APPLE IPHONE 5
Height: 123.8 mm (4.87 inches)
Width: 58.6 mm (2.31 inches)
Depth: 7.6 mm (0.3 inches)
Weight: 112 grams (3.95 ounces)
Touchscreen: 4in
Pixel density: 326 per inch
Display: 1136x640 pixels
Network speeds: 3G and mobile 4G
Camera: 8 megapixel in back-facing camera 1.2 in front-facing
Voice recognition: Siri upgraded to allow spoken recommendations for films or restaurants. Possible to update Facebook status by voice command
Built-in apps: FaceTime; video editing; Safari internet browser; email; Apple maps; no YouTube as standard
Processor: A6 chip said to be twice as quick as A5.
Internal memory: 16GB; 32GB; or 64GB
Other memory: Purchases stored in Apple’s iCloud servers
Battery: 1,400 mAh
Operating system: Apple iOS 6