Weeping residents combed through debris and stunned tourists wandered through litter-strewn streets on Monday, a day after tsunamis swept across the Indian Ocean from Thailand to Somalia, killing at least 23,000 people.

The giant waves -- caused by the most powerful earthquake on Earth in 40 years -- also left thousands injured and missing as well as hundreds of thousands homeless in Indonesia, India, Sri Lanka and Thailand.

The magnitude 9.0 quake struck about 7 a.m. Sunday (7 p.m. ET Saturday) and was centered about 100 miles (160 km) off the coast of Indonesia's Sumatra island at a depth of about 6.2 miles (10 km).

It was the strongest earthquake on Earth since 1964 and tied a 1952 quake in Kamchatka, Russia as the fourth strongest since such measurements began in 1899.

Asian officials conceded Monday that they failed to issue public warnings that could have saved many lives.

In Sri Lanka, where tidal waves swept ashore two-and-a-half hours after the initial earthquake struck Indonesia's Sumatra islands, The Associated Press said residents expressed disbelief that there was no warning. Residents and tourists woke Monday to shocking scenes: streets filled with rubble, cars shoved into store windows, piers and beach huts completely gone.

More than 12,000 people have been reported dead in Sri Lanka. Most of them were in the eastern district of Batticaloa, authorities said. Thousands are missing, an estimated 1 million are displaced and an estimated 250,000 are homeless.