Some 1.4 million people have joined a march demanding independence for the Catalonia region from Spain, Barcelona city police said.

Officials published the figure on Twitter after the demonstration, which marked the start of campaigning for a 27 September regional election billed by Catalan leaders as an indirect vote on independence.

The city police force, which is controlled by city hall, estimated turnout at 1.4 million.

Spanish government officials say half a million people are taking part in the march.

Waving red and yellow Catalan flags, they marched down a major road into the city, yelling "Independence!" while some formed human pyramids - a Catalan folk tradition.

The show of force on Catalan national day came at a time of high political tensions, some three months ahead of a general election in Spain, the eurozone's fourth-biggest economy.

State officials and other authorities did not immediately release their own estimates for turnout in Barcelona, capital of this region which counts 7.5m inhabitants.

Before the rally, organisers had said 500,000 people had signed up to take part.

At last year's Catalan national day demo, Spanish state officials and local authorities gave wildly different turnout figures for the politically-sensitive rally.

Polls this week showed pro-secession candidates could win a majority of seats in the Catalan parliament during this month's vote. 

If they win, Catalan president Artur Mas has vowed to push through an 18-month roadmap to secession for the region, which accounts for a fifth of Spain's economy.