Thousands of sun-worshippers have flocked to Stonehenge to celebrate the summer solstice, as the sun rises on the UK's longest day of the year.

Around 20,000 people gathered on Sunday morning to the neolithic site, located on Salisbury Plain in Wiltshire, to watch sun-up on the year's longest day to mark the ancient astronomical phenomenon.

Spectators were pictured standing around the monument's 'heel stone' or entrance to witness the 4.52am sunrise, with astronomical solstice itself is expected to occur at 9.24am.

Marking the occasion, visitors put on a purple light display before dawn, and were captured placing their hands on the ancient structure, playing traditional instruments and taking pictures in celebration as the sun began to stream through the morning fog into the centre of the stones.

Constructed around 3100BC, Stonehenge was built in accordance with the Northern Hemisphere's midsummer sunrise and the midwinter sunset. 

The summer solstice, which takes place on June 20 or 21st annually, occurs when the Earth's axis has its maximum tilt toward the sun as it reaches its highest position in the sky, ensuring the longest period of daylight for the year.

Solstices are widely believed to have been observed at Stonehenge for thousands of years, with Midsummer celebrations traditionally marked through outdoor events that include displays of dancing, bonfires and feasting. 

Georgia Butters, English Heritage's head of Stonehenge, said the summer solstice 'brings people together.' 

She said: 'Coming together at this iconic monument for the summer solstice is a tradition that brings people together from near and far.

'It was wonderful to see families and friends taking part in this joyous experience.

'We look forward to welcoming returning and new visitors to Stonehenge for next year's summer solstice.'

Elsewhere around the country, the beginning of summer solstice was marked from London to Suffolk and Glastonbury Tor in Somerset. 

On Parliament Hill in London, spectator Anna Dudziak viewed the sunrise for the first time as part of a Polish group that organises events throughout the capital. 

She told the BBC: 'The summer solstice is a big tradition in Poland, too, where it's celebrated with people dancing around a fire. It's celebrated a day after celebrations in the UK.'

At Glastonbury Tor, hundreds of spectators gathered on the hill as the orange sunrise appeared from behind the clouds. 

And revelers - including Stonehenge's sunworshippers - can expect hot weather to mark Britain's longest day as temperatures in Salisbury are set to reach 28C on Sunday.

The beginning of Midsummer has coincided with Britain's upcoming heatwave, with the Met Office issuing a severe high temperature warning for the East and West Midlands, east and south west of England, Wales and London. 

Forecasters predicted this week’s heatwave will be the hottest since the record-breaking summer three years ago.

Today is set to reach highs of 31°C (87.8°F) in London and South East England… but that's just the start of the tropical blast which is set to make Britain as hot as North Africa.

By midweek, temperatures could reach 38C (100.4°F), the warmest in three years since the all-time record of 40.3C (104.4°F) was hit at Coningsby, Lincolnshire, on July 19, 2022.

And the current highest UK June temperature, of 35.6°C (96.08F) recorded in Southampton in June 1976 and Camden Square in June 1957, is ‘likely to be broken’.

As the heatwave develops between tomorrow and Thursday, the Meteorological Office predicted ‘temperatures widely exceeding 35°C (95°F)’ in southern England and Wales – as hot as Tunisia - and rising higher still in some areas.

Forecasters warn the ‘severe weather event’ will affect public health, infrastructure, power and water supplies.

The sweltering heat could even cause tarmac to melt, as well as disrupting rail and air travel.

A Met Office spokesperson said: ‘The peak of the heatwave is now forecast for Wednesday and Thursday, when temperatures are expected to climb to 38°C. By Friday conditions will be less hot, with highs of 33°C (91.4°F) forecast across eastern England.

Forecasters also said overnight temperatures will also be very high – with widespread ‘tropical nights’, where the temperature does not drop below 20°C (68°F), across southern England.

The hottest areas are expected to be between Bristol and London and south of the M4 but Thursday’s temperatures are due to reach into the 30s as far north as York and Lancaster, and on the North Wales coast.

The Met Office added: ‘Humidity is also a factor, making this heatwave even more impactful with heat stress a danger to all.’

Amber extreme heat warnings have been issued from Monday morning through to Thursday night covering all of England except the North East, which has a yellow warning.

Met Office Deputy Chief Forecaster Tom Crabtree, said: ‘The combination of heat and humidity will be oppressive and bring impacts across society from public health and infrastructure to power and water supplies.’

People are advised to drink plenty of fluids, keep out of the sun and avoid exercising between 11am and 3pm, the Met Office said.

Met Office meteorologist Simon Partridge added: ‘It’s a very unusual, very rare spell of very hot weather, so it’s one of those ones where people should take care, try to keep their houses as cool as possible, check in on those that are vulnerable, so the very young and very old, in particular, are more vulnerable to extreme heat.

‘There’s also potential for impacts to transport as well. We know that when things get very warm, there can sometimes be issues with railway lines, and even possibility that some roads might not be doing too well. If it gets too warm, you may even see a little bit of tarmac melting at times.’

Officials are also concerned about ‘an increase in potential water safety incidents’ due to more people visiting coastal areas, lakes or rivers.

Fifteen people, many of them children, died after getting into trouble in open water during a hot spell in May.

Samantha Hughes, national water safety partner at the RNLI, said: ‘It’s important to remember that the water is still cold. Entering it unexpectedly can lead to shock.’

The Met Office said high temperatures are forecast to ‘persist through the week, especially in the southeast of England’.

It added: ‘There is some uncertainty in how long the highest temperatures will continue due to increasing cloud and thunderstorm risk.’

Europe is also sweltering under the heatwave, with highs of 40C (104F) expected in France today, where public alcohol consumption restrictions were put in place and sporting events cancelled.

Temperatures are predicted to reach 37C (98.6F) in Rome and 39C (102.2F) in Madrid tomorrow.