'Difficult': Prince William responds after soldiers faint at Trooping the Colour rehearsal

The moment a soldier fainted and another was carried away in a stretcher during a Trooping the Colour rehearsal as the UK sweltered was captured on video.

A member of the Massed Bands of the Household Division faints due to heat exhaustion during the Colonel's Review in London on Saturday. Source: AAP, EPA / Tolga Akmen

KEY POINTS

• The UK has sweltered through its hottest day of the year so far.
• Several soldiers fainted while taking part in a Trooping the Colour rehearsal ahead of the King's Birthday.
• Prince William acknowledged conditions were "difficult".

Several British soldiers fainted during a Trouping the Colour rehearsal as the United Kingdom sweltered through its hottest day so far this year.

Thousands turned out at St James Park in London to watch the Colonel's Review led by Prince William, the heir to the throne. The event saw him review more than 1,400 troops of the Household Division and the King's Troop Royal Horse Artillery to ensure they are ready for Trooping the Colour — an event held each June to mark the monarch's official birthday.

But the heat proved too much for some guardsmen, who were dressed in woollen tunics and bearskin hats, with at least three fainting, London's Evening Standard newspaper reported.

In one video, a trombonist is seen on the ground as medical personnel rush over to him with a stretcher.

He picks himself up before attempting to play on but is ultimately led away.

Another soldier was seen being carried away on a stretcher.

A trombone player of the military band is carried out on a stretcher after a fainting during the Colonel's Review on Saturday. Source: AAP, AP / Alberto Pezzali

The Prince of Wales carries out the Colonel's Review at Horse Guards Parade in London on Saturday. Source: AAP, EPA / Tolga Akmen

“A big thank you to every solider who took part in the Colonel’s Review this morning in the heat. Difficult conditions but you all did a really good job. Thank you. W," the Prince of Wales tweeted.

It came as the UK Health Security Agency issued an amber heat-health alert, that warns of high temperatures that are likely to affect most of the population and impact health services, for eastern and southern England, and the Midlands.

According to the BBC's lead weather presenter, Simon King, temperatures hit 30.4C in some parts of England, which made Saturday the hottest day of the year so far.

The Trooping the Colour ceremony will be held on 17 June in the UK.

Most parts of Australia will mark the Kings Birthday on Monday 12 June with a public holiday, except for Western Australia where it is celebrated at the end of September, and Queensland, which marks the occasion on the first Monday of October.