Three people were shot dead in day-long chaos on Friday as NASA leader Raila Odinga returned from the US to a hero's welcome that degenerated into blood and tears.
There were running battles, burning vehicles, tyres and barricades, tear gas, blasts from water cannon and suspected live bullets.
Thousands of supporters defied a ban on demonstrations.
The windscreen of Raila's bullet-proof Range Rover car was smashed by a rock or a bullet at the Uhuru highway roundabout.
The former Prime Minister was inside but uninjured.
NASA said this was an attempt on his life.
At Upper Hill, Raila addressed supporters as he wiped his eyes, watering from tear gas.
“I am very angry today. My anger is with this boy called Uhuru Kenyatta," he said, who heads a crumbling regime.
"I have come back home from abroad. He sends police to teargas me, beat up my people and shoot them. This is being beastly."
The Third Liberation is coming and Canaan is near, Raila said.
“What you have seen are signs of a collapsing government like that of [Zimbabwean President Robert] Mugabe. He thought he would leave the presidency to the wife but he is under house arrest... Tell Uhuru bye bye,” Raila told jubilant supporters.
NASA co-principal Kalonzo Musyoka is to jet in to Nairobi on Saturday from from Germany.
Opposition supporters pledged to stage another day of ddemonstrations, like those witnessed on Friday.
As the trouble started, police made several attempts to block thousands of supporters from entering JKIA and escorting Raila along city streets. They also blocked city roads to stop the procession.
Police fired tear gas and used water cannon as they tried to stop the convoy from reaching the main business district. Protesters threw stones and set fire to a police lorry on fire along Landhies Road.
The deaths occurred as police and protesters fought on Jogoo and Landhies roads, Star reporters said.
Police spokesmen did not immediately respond to phone calls.
On its Twitter handle, NASA claimed there was an attempt on Raila's life when he got to Jogoo Road and after his supporters overpowered the police.
"Raila Odinga has survived an attempt on his life while driving into town from JKIA, following his arrival from the US this morning. Fortunately he and all co-passengers are well owing to his state-of-the-art bullet-proof car," it said.
Upon arrival aboard a Kenya Airways flight from Dubai, the opposition chief left the airport in a convoy of tens of vehicles accompanied by a host of NASA leaders and hundreds of supporters.
They greeted him with a guard of honour.
Chaos erupted immediately the convoy left the airport, with Raila's vehicle taking the wrong side of Mombasa Road because the route was gridlocked for kilometres.
The day unfolded like a Hollywood action movie.
Police fired several times in the air and used water cannon as they tried to prevent it from reaching the CBD.
They blocked all roads into the city and halted the convoy at Nyayo Stadium, forcing supporters to move to Jogoo Road through Likoni Road.
Raila's car was sandwiched between three security cars while those of co-principal Musalia Mudavadi and other leaders followed.
At Jogoo Road they were met with clouds of tear gas and water cannons.
There police retreated twice after they were overpowered by thousands of NASA supporters trying to get to Uhuru Park.
They set ablaze two matatus next to City Stadium after police retreated to the Jogoo Road roundabout.
For over four hours, Jogoo Road was a no-go zone as NASA backers engaged police in fierce running battles.
At one point NASA leaders managed to get into City Stadium, but police flushed them out, forcing them to regroup and force their way through Jogoo Road to the city centre.
Supporters set fire to two matatus next to City Stadium after police retreated.
Raila's supporters shielded his car as the convoy snaked through Haile Selassie Avenue towards Uhuru Highway before they were met with a hail of bullets.
For over four hours Jogoo road was a no-go zone as NASA backers engaged police in fierce running battles.
Raila's supporters shielded his car as the convoy snaked through Haile Selassie avenue towards Uhuru before they were met with a heavy hail of bullets.
As police fired fiercely the NASA leaders drove towards Ngong road towards Kamukunji grounds Kibera in a last ditch effort to address his supporters after police.
The Star