SCIENTISTS are probing a chemical substance this afternoon which has closed a road home to a psychiatric hospital.

A cordon has been thrown round Monks Orchard Road, in Beckenham, since the alarm was raised at about 10.15am.

Residents and staff and patients at the Bethlam Royal Hospital have been told to stay inside with their windows and doors closed.

The substance is described by firefighters as a "spillage" and by witnesses as a pool of water "with a lot of white froth in it".

A spokesman for South London and Maudsley NHS Trust, which runs the Bethlem, said: "We have been taking avice from the fire and police authorities.

"The position at the moment is that we have been told to keep the windows and doors closed. We're hoping for an update this afternoon."

He added: "It has caused some difficulties with people leaving the site and not being able to get back in again.

"We do have a back entrance. Our teams are down there ensuring that people are able to get where they need to go."

A London Fire Brigade spokesman could not confirm whether there have been any evacuations or how big the cordon is.

He added: "Our scientific support unit is down there at the moment assessing the situation. The incident is ongoing.

"The road is closed and we will be assessing which other roads need to be closed."