Four killed in Welsh refinery blast

"Mid and West Wales Fire and Rescue Service received a call (Thursday) at 18:22 pm (17:22 GMT) reporting an explosion at Chevron Oil Refinery at Pembroke Dock," chief superintendent Gwyn Thomas said in a statement.

"Paramedics have confirmed that four people lost their lives as a result of the incident," continued the Dyfed Powys police statement.

According to the force, a 730 cubic metres storage tank exploded while maintenance work was being carried out.

A police investigation was launched Friday into what Thomas described as "a tragic industrial incident".

Around 50 fire fighters extinguished the resulting blaze, the fire service said.

"Crews from Mid and West Wales Fire and Rescue assisted the onsite Chevron fire personnel throughout the operation," assistant chief fire officer Chris Davies said in a statement.

"The fire itself was extinguished quickly and the crews worked to make the scene safe for police to start their investigation," he added.

Chevron earlier released a statement saying "all appropriate action" had been taken in response to the situation.

Nearby Morriston Hospital in Swansea said it was treating an injured man.

"One casualty, a male, has been received and admitted to the hospital. No information on his condition is currently available," the hospital said.

"Anyone with minor injuries from the incident are expected to be treated at hospitals closer to the scene."

A witness described how a thick plume of smoke could be seen for kilometres (miles) around.

"I was leaving the site at the end of the day and I could hear explosions and see plumes of smoke," he told the BBC.

"You could see flames on the pipework from across the valley," he added.

Joanne Lutwyche, who lives near the west Wales plant, said: "Quite a few people in the village work at Chevron and would have been changing shifts when the explosion happened, so everyone's really concerned for who might be involved.

"The last time something like this happened must have been about 17 years ago," she added.

Fire fighter Chris Davies reassured local residents that any material released into the atmosphere as a result of the blast had "immediately dispersed" and posed "no ongoing risk to health".

The refinery, which employs 1,400 people, was due to change hands after Valero agreed earlier this year to buy it for 730 million dollars (503 million euros).

Copyright AFP (Agence France-Presse), 2011