A junior minister for health, Channa Jayasumana, called the Delta variant of the virus “a powerful bomb which has exploded in Colombo and is spreading elsewhere”.
On Friday the government tightened some restrictions, banning state ceremonies and public gatherings until Sep 1.
But most activity is allowed, with shops, restaurants and offices open and public transport still operating.
The number of deaths hit a record 111 on Monday with the daily average in the past week crossing 100 — more than double the average of 40 in the previous week.
The number of infections also more than doubled to nearly 3,000 this week.
At one morgue in Colombo on Tuesday morning, workers tested 15 bodies for COVID-19 and then cremated them to clear the way for more bodies.
A Colombo magistrate ordered the immediate disposal of 40 bodies that remained unclaimed by the next of kin.
The Colombo Municipal Council began mass cremations Sunday to clear a backlog after hospital mortuaries ran out of refrigeration space for bodies.
Just over 11.2 million people out of the population of 21 million have been given at least one vaccine jab, while 3.2 million had received both as of Monday.
Sri Lanka has recorded 5,222 deaths to date and almost 333,000 infections, according to official data.