JAKARTA, Jan. 22 (Xinhua) -- A shallow undersea earthquake measuring 6.7 magnitude struck off East Nusa Tenggara province of central Indonesia on Tuesday, but there was no tsunami alert issued, the country's meteorology and geophysics agency said.

The tremor was the main shock of a series of quakes that hit the region on Tuesday. A 6.2-magnitude quake and two 5.2-magnitude ones that happened earlier in the day were determined to be foreshocks, official in charge of the agency Priyo Budi told Xinhua by phone.

The main shock jolted at 12:10 p.m. Jakarta time (0510 GMT) with epicenter at 120 km southwest Sumba Barat district of the province and with a depth of 10 km under the sea bed, Budi said.

"Our observation on the quake, so far, there is no potential for tsunami from happening," he said.

The intensity of the quake was felt at 3 MMI (Modified Mercalli Intensity) in Waingapu town of the province, Budi said.

For the 6.2-magnitude foreshock, its jolts were felt strongly at 4 to 5 MMI in Tambolaka town of the province and 3 MMI in Waingapu town of the province, Aziz Sugiarso, another official of the agency told Xinhua earlier.

The jolts were also felt at 3 MMI in nearby province of West Nusa Tenggara, in Bima town and in Sumbawa district, he said.