US President Barack Obama was one of the first to arrive at the Excel Centre

World leaders are arriving for the G20 summit in London where they will strive to agree measures to tackle the worst financial crisis since the 1930s.

US President Barack Obama was one of the first to be greeted by UK Prime Minister Gordon Brown.

The G20 is expected to strengthen banking regulation to try to prevent a repeat of the crisis in the future.

Extra efforts to boost economic growth will be agreed, but specific targets on government spending look unlikely.

More demonstrations are expected after protests in London on Wednesday.

One man collapsed and died at the protest, police said, and at least 87 arrests were made.

There is tight security at the Excel Centre in London's Docklands where the summit is being held.

Members of the media were reporting hold-ups in gaining access to the venue as police carried out extra security procedures.

A small group of protesters have begun to gather at the London Stock Exchange, where a BBC correspondent says they are far outnumbered by the number of police officers.

'Deal close'

Leaders are beginning the day with a working breakfast. Four and a half hours of talks will then begin in earnest.

WHAT TO LOOK FOR Concrete powers for international financial regulator Increase in IMF fund to at least $500bn (£345bn) Measures to boost trade More aid for developing countries Less likely: Targets for additional stimulus spending

In the run-up to the summit, the main differences have been between France and Germany, who are seeking stricter regulation of the financial system, and the UK and US, who think extra government spending would do more to ease the crisis.

France's president, Nicolas Sarkozy, has threatened to walk out of the meeting if the G20 does not come up with concrete results and on Wednesday, Mr Sarkozy made it clear he was unhappy with the draft agreement.

However, BBC economics editor Stephanie Flanders says that the G20 is close to an agreement.

The main disputes are financial rather than ideological, our correspondent says.

Extra funds

More money is likely to be given to the International Monetary Fund, to help developing countries in difficulty.

The head of the IMF, Dominique Strauss-Kahn told the BBC that in addition to increasing funding for his organisation, he thought dealing with banks' toxic assets - which caused the world's credit markets to freeze up - must be a priority.

"I am worried about how the balance sheets are going to be cleared up, this cleansing of the balance sheet is the problem we really need to address now."

The summit is expected to push for closer supervision of hedge funds, private equity firms and derivatives trading. Tax havens are also likely to be targeted.

'Balancing act'

Leaders will release the final communiqué, which outlines their agreement, at around 1530 BST.

"This is by no means the end of the process", BBC chief economics correspondent Hugh Pym warns. "The G20 will need to meet again."

SUMMIT SCHEDULE 0730 G20 leaders begin arriving at the Excel Centre, East London 0830 Summit starts with working breakfast 1530 Closing statement by Brown 1745 Obama closing press conference All times BST

He says the leaders will have a difficult balancing act in presenting the final agreements later on Thursday.

There will have to be a bit of pragmatism over what can and cannot be achieved, our correspondent says, but they must also convey a sense that they really have a vision as to how they can bring economies through this recession.

The recession has worsened since G20 leaders met last November in Washington.

Both the IMF and the World Bank expect the world economy to shrink for the first time in decades this year.

Reporting from from the Excel Centre, BBC business correspondent John Moylan said the summit would be judged a success if the global recession became a short, sharp shock, rather than a very long downturn.

The G20 group of nations is made up of the world's most powerful economies, accounting for 90% of the world's economic output, 80% of world trade and two-thirds of the world's population.

Source: BBC News