HS2 tunnel fire: Workers shelter in digger near Maple Cross

The Chiltern Tunnel is being constructed as part of the HS2 rail line between London and the Midlands

An investigation has begun after a fire in a tunnel being constructed for the HS2 high-speed rail line.

The "small" fire on Tuesday evening involved a vehicle used to ferry staff in and out of the Chiltern Tunnel near Maple Cross in Hertfordshire.

HS2 Ltd confirmed three workers took shelter on a tunnel boring machine in a safety chamber and nobody needed hospital treatment.

It said the tunnel was safely evacuated once the fire had been put out.

An HS2 spokesperson said: "We can confirm that the emergency services attended an incident at the HS2 Chiltern Tunnel South Portal site yesterday evening.

"An investigation into the incident is ongoing. All personnel are safe and accounted for."

A Hertfordshire Fire and Rescue Service spokesperson said: "Having established that everybody was safe, firefighters worked with the on-site specialists to extinguish the fire and ventilate smoke and gas from the tunnel. Firefighters remained on site overnight."

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The boring machine was not damaged by the fire, which was about a mile (1.6km) away, and the company said staff followed usual safety procedures by staying in a safety chamber until the incident was under control.

HS2 is a multi-billion-pound project intended to create high-speed rail links between London and major cities in the Midlands and North of England.

The 16km (10 miles) Chiltern Tunnel is the longest tunnel on the section between the capital and Crewe.