MECCA, Oct 24 (Reuters) - Nearly 3 million Muslim pilgrims started the first phase of the annual haj on Wednesday, travelling through packed streets from Mecca's Grand Mosque to the enormous camp at Mina just outside the Saudi Arabian city.

In a dense sea of humanity, all clad in the same simple white robes, the pilgrims who were unable to get onto a new rail link were packed into 18,000 buses provided by the city or perched on the roofs of trucks. Others walked the 5 km to Mina in late afternoon temperatures of 35 degrees Celsius.

"I want to ask God for paradise... I don't want anything from the world. I want to win paradise and be among good men," said Abdul Raki al-Yamani, a Yemeni who lives in Mecca, waiting to mount a bus.

Islam's pilgrimage is one of the faith's so-called five pillars and is a duty for all Muslims once in their lives if they are capable of it.

The mayor of Mecca, Osama Fadl al-Bar, said he expected the number of pilgrims this year to be close to 3 million people, including those from inside Saudi Arabia. The Interior Ministry said 1.75 million had arrived from abroad.

This year haj comes against a backdrop of division in the Middle East, a historic centre of the Islamic world, as Shi'ite Muslim Iran and Sunni countries like Saudi Arabia and Turkey back opposing sides in Syria's civil war.

Riyadh and Tehran have both played down the prospect of politically related trouble at the haj, but Saudi authorities have warned they will not allow disruptions.

In some previous years the haj has been marred by disasters, including stampedes and tent fires in which hundreds were killed. But the authorities have invested heavily in better infrastructure and there have been no such incidents since 2006.

On Thursday the pilgrims will travel a further 7 km to Mount Arafat, a rocky hill where they must stand in prayer, a moment many Muslims see as the climax of the haj.

Hussein Ali, 37, a Syrian who lives in Kuwait, decided to walk from Mecca to Arafat.

"I start marching to Arafat after midnight where it should take about three hours," he said.

They will then spend the evening on the plains of Muzdalifah where they must pick up pebbles used the following day to hurl at three large walls representing Satan in Jamarat, between Mecca and Mina.

"Arafat is the greatest pillar of the haj and I hope the Lord will accept my prayers there. I hope I have enough money so I can come here again so I can repent my sins," said Mohammed Omar Emara, 33, a fisherman from Egypt.

He travelled for three days by bus to reach Mecca after his father gave him money to make the journey.

"I am happy to be here so I can repent my sins in this old house of God and the good deeds are doubly rewarded here," Emara said, as he walked in Mecca's Aziziyah neighbourhoods in search of a grocery shop to stock up on bread and water for the journey. (Reporting By Mahmoud Habboush; Editing by Angus McDowall and Paul Casciato)