Many roads in the capital were sealed off and mobile phone providers shut down their text messaging services during the ceremonies.
The Sri Lankan military is on high alert after three bombings over the weekend which were blamed on the LTTE.
The LTTE says it has been fighting for more than two decades for a separate homeland for the country's minority Tamils.
Officials had said that the armed forces were expecting the Tigers to attempt attacks.
"There have been recoveries of suicide jackets and an LTTE cadre [fighter] last week. They are trying to disrupt the independence celebrations," Brigadier Udaya Nanayakkara, military spokesman, said.
"We are expecting some kind of sabotage activity from the Tigers."
The US embassy advised American citizens to avoid unnecessary travel in and around the capital during the holiday because of fear of attacks."We faced this challenge squarely without avoiding it. Our security forces are today achieving victories against terrorism unprecedented in history," he said.
Earlier, thousands of police and other security forces took up position in Colombo as the celebrations got under way with Mahinda Rajapakse, Sri Lanka's president, raising a national flag on the seafront.
A display of military might followed, with Rajapakse reviewing a parade of troops and tanks on Colombo's Galle Face road as fighter jets flew overhead.
The "challenge bestowed upon us by history is the defeat of terrorism", he said.
Rajapakse said that the military now had the LTTE fighters cornered in the north of the island.
|A suicide bomber blew herself up at Colombo's|
main railway station on Sunday [Reuters]
Sri Lanka's government formally pulled out of a Norwegian-brokered truce with the LTTE last month.
A suicide bombing at the capital's main railway station on Sunday was preceded by an attack at the city's zoo which injured at least six people.
Early on Sunday, an electricity substation was destroyed by a bomb but there were no injuries, the military said.
A more powerful bomb was found and defused in the same area several hours earlier, police said.
On Saturday, an explosion on a bus in the central town of Dambulla, about 150km northeast of Colombo, killed at least 18 people.