Dr Anil Jasinghe of the Colombo National Hospital said eight people died before they arrived at hospital and two police officers "succumbed after admission".
He said about 85 people are being treated for injuries.
Reports quoting witnesses spoke of a loud explosion in Colombo's commercial quarter and black smoke rising from an area near the Hilton Hotel.
The area is home to the official residence of Sri Lanka's president, besides the Hilton Hotel and the twin-tower World Trade Centre office complex.
Udaya Nanayakkara, a Sri Lankan military spokesman, said government officials had recovered a larger number of explosive devices from LTTE strongholds, "so we are progressing very well."
'Most secure areas'
Speaking of Friday's suicide attack, Minelle Fernandez, Al Jazeera's correspondent in Sri Lanka, said: "This is one of the most secure areas and one of Colombo's most commercial hubs, where the bomb exploded.
"Though there is a visible security presence in that area, the fighters just have to get lucky once to be effective.
"People in Colombo were expecting a very large demonstration today, and that's why the explosion occurred.
"It seems the capital is very vulnerable to such attacks but, even worse, civilians are being caught up in this civil conflict."
The LTTE has not commented on the incident, but it routinely denies responsibility for such attacks.
The blast is the first suicide attack since April 6 when a bomber killed 14 people, including a government minister and a former Olympian, at the start of a marathon in the capital.
LTTE base bombed
Friday's attack in Colombo came a day after air force fighter jets bombed a Tamil Tiger base in the northern jungles.
The military says 27 fighters and two government soliders were killed in the fighting in the Vavuniya, Mannar and Jaffna regions on Thursday.
Early on Friday, air force jets bombed a base of the Sea Tigers, the LTTE's naval wing, in their de facto state in the north, Andy Wijesuriya, a military spokesman, said.
Another LTTE base in Mullaitivu was struck overnight he said.
Wijesuriya did not give details of casualties or damage, but said "pilots have confirmed they hit the target accurately".
It is not possible to independently verify the military's claims because reporters are not allowed in the war zone.