Police said about 120,000 people, many from government offices and Christian groups, came to Manila's Rizal Park under hazy skies to back Gloria Macapagal Arroyo in what was billed as a "gathering for peace and unity for the rule of law".
Banners read "President Arroyo please stay" and "God bless the president and the Philippines".
Steadied by a few key allies, Arroyo has dug in her heels to ride out mass resignations and defections that a week ago appeared to be driving her four-year presidency to a rapid end.
The opposition accuses Arroyo of cheating her way to victory in the 2004 election and her family of corruption. She has denied wrongdoing but now faces the threat of impeachment by Congress, a prospect that worries financial markets.
"It does not matter how many rallied for Arroyo," said Joseph Roxas, president of Eagle Equities in Manila.
"Since the opposition did not muster enough numbers to cause alarm, it has had to shift the battlefield to the impeachment process in Congress."
Manila Mayor Lito Atienza, an Arroyo loyalist, earlier denied reports that city workers were promised 2000 pesos ($35) each to attend.
Beefing up a rally is fairly common in the Philippines, with people taking a fast-food meal and usually a couple of hundred pesos to march and chant. Film stars, dancers and thumping music keep the crowd entertained between speeches.
Arroyo is accused of cheating her
way to victory in the 2004 poll
Arroyo was not expected to attend Saturday's event. But the large crowd in the midst of the crisis will help her reinforce the image of a president focused on running the country and reforming the economy with the support of the people.
The opposition fell short of its target on Wednesday with a crowd of 30,000 political opponents mixed with groups of leftists, students and farmers in Manila's business district.
Bigger protests have been promised around 25 July, when Arroyo is to deliver an annual state of the nation address.
Arroyo's political enemies concede she is unlikely to be dislodged by marches nowhere near the size or social breadth of "people power" uprisings that overthrew Ferdinand Marcos as dictator in 1986 and Joseph Estrada as president in 2001.
Instead, they are warming to the idea of trying to impeach her in Congress as shifting party loyalties threaten her majorities in both houses.
Joseph Estrada was ousted as a
result of 'people power' uprisings
Another way out of the crisis has been proposed by influential former president Fidel Ramos, who envisions a parliamentary system after changes to the constitution. Arroyo would stay on as caretaker until elections next year.
Arroyo's aides have said she is seriously considering the Ramos plan.
An impeachment motion needs 79 votes, or one third of the lower house, to progress to a trial by the upper house's 23 senators. An impeachment conviction in the Senate, effectively sacking the president, needs two-thirds of the senators' votes.
Weeks of political turmoil have kept investors nervous and raised fears that a protracted impeachment battle or constitutional debate will paralyse reforms aimed at raising revenues and cutting debt.
But financial markets were lifted on Friday by expectations the Supreme Court will soon end its freeze on a broader sales tax that is at the centre of the government's reforms.
Investors also took heart from a monthly budget surplus in June, the second this year.
Elsewhere, Muslim separatists opened fire on two military helicopters in the southern Philippines, wounding a soldier, the Philippine military said on Saturday.
A Moro Islamic Liberation Front (MILF) spokesman claimed Friday's attack forced one of the aircraft to crash-land near the town of Talayan on Mindanao island, but the military denied this.
A ceasefire had been observed
ahead of peace talks
The two sides had been observing a ceasefire for two years ahead of peace talks planned in Malaysia this month.
"Gunfire from the ground" wounded a soldier on board a military helicopter on Friday, and he is now "recovering from his wounds in a hospital," air force spokesman Lieutenant-Colonel Restituto Padilla told ABS-CBN television.
The helicopter has been brought to a military hangar and "maintenance people are working on it," Padilla said, denying a MILF account that the aircraft was shot down.
Padilla said two military helicopters were attacked as they ferried combat troops into the province of Maguindanao to hunt down members of the Abu Sayyaf, linked by western intelligence agencies to the al-Qaida network.
The gunfire "came from the MILF positions" and not those of Abu Sayyaf, he added. He said the military leadership had alerted the government's peace negotiating panel about the ceasefire violation.