Battersea's London Heliport was forced to close for 30 hours when a potentially explosive cylinder was dropped at a site next door.

Firefighters were at the scene from 10.30am yesterday until about 4pm today, where they used thermal imaging cameras to monitor the cylinder's condition every hour.

There were two cylinders, containing oxygen and acetylene, resting on the riverbed in shallow water, meaning a fire boat also had to be in attendance. It is believed the cylinders, which are used for industrial cutting, were linked to a boat refurbishment at the site. A Fire Brigade spokesman said: "The shock to the cylinder means it can begin to disintegrate over a 24-hour period. It could possibly become explosive."

Police closed the heliport and Lombard Road yesterday, although the road re-opened later in the day.

Firefighters anticipated the heliport would also re-open by 11am this morning because the tide would submerge the cylinders, cooling them down and so reducing the risk. However, firefighters from Clapham's white watch remained at the scene until mid-afternoon when it was finally declared safe.

The heliport was unavailable for comment.