* Tshisekedi blocked at airport by police
* At least two dead amid rock-throwing, gunfire
* Elections are second since 1998-2003 war (Adds Tshisekedi leaving airport)
By Jonny Hogg and David Lewis
KINSHASA, Nov 26 (Reuters) - Police in Congo blocked President Joseph Kabila's main rival at an airport in Kinshasa on Saturday to stop him staging an election rally after at least two died in violence across the central African state's capital city.
Two days before presidential and parliamentary elections, rival factions hurled rocks at each other and gunfire was heard across town.
A Reuters reporter saw one lifeless body on the road to the airport while a U.N. source reported another death elsewhere in town.
The violence was the latest sign of tension in the run-up to Congo's second election since a 1998-2003 war, a poll which has been marked by opposition allegations of irregularities and concerns about inadequate preparations.
Police stopped opposition leader Etienne Tshisekedi and his entourage from leaving Kinshasa's N'djili airport after his party said it would defy a ban on political rallies imposed earlier on Saturday.
"I'll call the population of Kinshasa to come here," Tshisekedi, 78, sitting in a red Hummer surrounded by police at the exit gate of the airport, told reporters.
"We are already dying in our thousands, we are not going to let a few injuries stop us fighting now," he said, a reference to his accusations that Kabila's government has saddled Congo's population with insecurity and poverty.
After hours of failed negotiations by the United Nations peacekeeping mission, police moved in on Tshisekedi's entourage, dragging several people from their cars, according to a Reuters witness. Tshisekedi was later escorted to his home by the police, according to a U.N. source.
Earlier, tens of thousands of Congolese turned out on the airport road, most of them identifiable as Tshisekedi supporters. Some chanted his name while many billboards for Kabila and his allies had been torn down.
Kabila, Tshisekedi and the other main challenger, Vital Kamerhe, had been due to hold rallies within several hundred metres of each other in central Kinshasa on Saturday.
Kamerhe told Reuters that four people had been killed, including one of his supporters, but it was not immediately possible to confirm that toll.
Under constitutional amendments signed off by Kabila this year, the presidential vote will be decided in a single round, meaning the winner can claim victory with a simple majority. Analysts say that favours Kabila against the split opposition.
Despite a logistics operation supported by helicopters from South Africa and Angola, some observers doubt whether all the ballot slips will reach the 60,000 voting stations by Monday in a country two-thirds the size of the European Union.
However national election commission president Daniel Ngoy Mulunda said he did not expect any delay to the polls, saying that materials were 90 percent deployed in the provinces.
"No, I am not expecting any change. We have today, the whole night, tomorrow day and night to finalise (preparations)," Mulunda told a news conference in Kinshasa.
"We had some delays with weather but we know it will work - on Monday it won't rain."
Earlier, Tshisekedi said he could accept a delay but only if Mulunda, whom he accused of having political ties to Kabila and turning a blind eye to alleged irregularities, was sacked.
"I would agree (to a delay) if that meant a more credible, democratic and transparent process," he told French RFI radio.
"But one thing is clear: if we say there will be a delay, it is clear that the election commission cannot be led by Daniel Ngoy Mulunda," he said, accusing him of having been a founding member of Kabila's PPRD political party.
Mulunda, who will have the deciding vote if his commission is split on any election dispute, said this week he did not deny having been a member of the delegation that accompanies Kabila on foreign trips, but said he was not a founding PPRD member.
Kabila's rivals say fake polling stations have been set up to allow vote-rigging, an allegation denied by the authorities. They also accuse Kabila of using state media and transport assets for his campaign.
Kamerhe said the Congolese would not accept a rigged poll.
"They want free and fair elections that allow them to take their destiny in their own hands. People will refuse cheating wherever it takes place," he told Reuters, surrounded by chanting and dancing supporters at his party headquarters.
For many Congolese, there was a last-minute scramble to find out where they should be voting. Gervis Ilunga, a 44-year-old security guard, said he registered in one Kinshasa district but ultimately found his name elsewhere.
"In 2006, things were at least organised," he said of the first post-war poll largely organised under the auspices of the United Nations. "It is not like that this time ... There will be too many challenges this time." (Additional reporting by Finbarr O'Reilly; Writing by Mark John; Editing by Sophie Hares and David Cowell)