FIFA president Sepp Blatter has played down concerns over Brazil's hosting of the World Cup by saying he's never known a host nation get everything ready on time.

Blatter, who was greeted by placard-wielding protesters in Hong Kong, urged people to be "optimistic" about the June-July event despite construction delays and demonstrations.

"This is my 10th World Cup since I have joined the FIFA organization and I have never seen a World Cup that has everything ready on-time during that span," Blatter said on Thursday, according to a statement from the Hong Kong FA.

"Four years ago, I remember people said that we should not have gone to South Africa and that people should be wearing bullet-proof vests when they are on the street.

"I urge you to be optimistic as we are optimistic. Football is stronger than any outside power as it is being played everywhere in the world, and I believe it is going to be a great World Cup tournament in Brazil."

Blatter's visit to inaugurate the HKFA's new offices was disrupted by about a dozen people protesting against construction worker deaths in 2022 World Cup host Qatar.

He used a back entrance to sidestep the demonstration and his address was nearly drowned out by the protesters shouting slogans over loudspeakers, the South China Morning Post said.

Brazil's World Cup has been plagued by delays to stadium and infrastructure projects and sizeable public opposition to investing in the tournament rather than basic services.

And Qatar has come under fire for its treatment of migrant workers with the International Trade Union Confederation warning that as many as 4,000 might die by the time the tournament kicks off.