Scotland Yard said there were no reports of any injuries, but anti-terrorist officers were continuing to check the area when there were reports of another suspect package in the vicinity.
Yesterday senior Sinn Fein negotiator Martin McGuinness had practically ruled out any early resumption of the IRA ceasefire, in terms which appeared to preclude the inclusion of his party in the coming political negotiations.
Last night a police spokesman said: "Police received a coded warning at 22.22 this evening 24 April, stating there was a device on the south side of Hammersmith Bridge. Police immediately evacuated and cordoned off the area and began a search.
"At 22.54 a small explosion occurred in the vicinity of the south side of Hammersmith Bridge."
The London office of Associated Press (AP) received two telephone warning calls from a caller claiming to represent the IRA. Local residents said what sounded like two blasts close together followed more than 30 minutes later, after the bridge had been cleared and blocked off.
Staff and customers at the Blue Anchor pub in Hammersmith, near the bridge, reported hearing "two loud bangs". Pub manager Kevin Martin, 23, said: "There were two really loud bangs so I went outside to go and have a look."
Mr Martin said the explosions went off shortly after 11pm as staff were clearing customers from the pub on Lower Mall in Hammersmith. "Everyone in the pub was talking about the bangs but there was no panic, people were pretty calm about it."
London has seen a series of relatively small-scale IRA bomb strikes over recent weeks, in the wake of the massive blast at South Quay in Docklands, east London on 9 February. That explosion, which killed two people and caused many injuries, signalled the end of the IRA ceasefire. It had been formally announced minutes before.
Last night's incident came almost exactly a week after the last explosion in London, at The Boltons near Earl's Court in west London. It went off just before 10pm on 17 April, just as anti-terrorist police began searching the area after a coded message, described as vague, was again telephoned to AP. Only minor damage was caused to the house, which was empty and undergoing building works, and no one was hurt.
Bombings such as those in Hammersmith appear to be designed as little more than nuisance explosions to remind the authorities of the IRA's violent capabilities in Britain. The intention seems to be to avoid civilian casualties, but to deliver the message that the IRA can strike at will in the capital.
Scotland Yard said last night's blast was not a controlled explosion: "We believe at the moment it was just one blast. Possibly an echo would account for reports of a second explosion."
The blast followed a warning earlier in the day from Sinn Fein that no early resumption of the IRA's ceasefire was to be expected.
Although last night's incident was the latest in a series in London, Northern Ireland has itself been free of IRA attacks since the ceasefire broke down in February.Reuse content