Firefighters are investigating the cause of a blaze which closed a major road last night.

Herts Fire and Rescue sent three fire engines to tackle the fire at Brookdell Yard, off St Albans Road, Garston at around 8.20pm (April 30).

Crews found an outbuilding “well alight” but were able to extinguish the flames by 9pm. They then remained at the scene until 10pm to damp down the area.

Watford Observer: Smoke above Garston last night.Smoke above Garston last night. (Image: Contributions)

Just before 9pm, police in Watford shared a message alerting motorists that the A405 St Albans Road had been closed between Bricket Wood and Garston, while firefighters tackled the blaze.

Herts Police officers were also on the scene to assist.

Watford Observer: Smoke above Garston last night.Smoke above Garston last night. (Image: Contributions)

Today, a Herts Fire and Rescue spokesperson said: “Our fire investigation team will be working with police this morning to help establish the cause of the fire.”

Rising smoke could be seen from across the Garston area and beyond last night, with pictures showing thick clouds of "very dark" smoke.