Odisha, which has been pummelled by heavy rainfall over the past week, is bracing for a medium flood in the Mahanadi river system with the formation of another depression over the Bay of Bengal, the Meteorological Centre in Bhubaneswar said on Sunday.

A well-marked low pressure system that intensified into a depression over the northwest Bay of Bengal has crossed the coast near Digha in West Bengal between 10.30-11.30 am, triggering heavy-to-very-heavy rain in many coastal, northern and southern regions of Odisha.

The weather system, which lies about 70 km northeast of Balasore, is moving northwestwards and is set to maintain its intensity for the next 24 hours, the meteorological centre said.

As the intensity of rain has increased in parts of the state, including the upper catchment area of river Mahanadi, the state government is anticipating a "medium flood" this time, said Special Relief Commissioner (SRC) P K Jena.

"We expect a flow of around 10.5 lakh cusecs of floodwater at Mundali barrage near Cuttack by Monday evening. Accordingly, we are preparing for a medium flood in the Mahanadi system," the SRC said, adding that people have nothing to panic for now as the administration had handled a similar situation in August, 2019.

Jena said that as much as 9.5 lakh cusecs of water were currently passing near Khairmal, downstream of Mahanadi, and that would require 24 hours to reach Mundali.

"Therefore, we expect peak flood in Mahanadi by Monday evening when above 10 lakh cusecs of water will pass," the SRC said, adding that district authorities have been asked to evacuate people from low-lying areas.

Jena, who reviewed the situation, said 22 rescue teams comprising the NDRF, ODARF and Fire Service personnel, have been sent to districts of Puri, Khurda, Kendrapara, Jagatsinghpur and Cuttack, as these places were likely to be more affected due to the possible flood.

He also explained that 34 of the 98 Hirakud reservoir gates have been opened for discharging water, noting that the lower catchment area received heavy showers in the last 12 hours.

Official sources said that Mahanadi's tributaries such as Luna, Karandia, Chitroptala, Daya, Bhargavi, Rajua and Malaguni were also swelling.

"Therefore, we cannot afford to open more gates of Hirakud now to discharge additional water," a senior official of the water resources department said.

Asked about the situation in other rivers, the SRC said, "There will be no flood in Baitarani, although the water level at Akhuapada was flowing at 18.06 metres against the danger level of 17.83m."

He pointed out that water level in Jalaka River at Mathani was also flowing at 6.39 metres, almost 0.9 metres above the danger level, but stressed that there was no reason to worry as of now.

In the last 24 hours till 8.30 am, Hemgiri in Sundargarh recorded 200 mm of rain, the highest in the state, followed by 168 mm at Astaranga in Puri, 167.4 at Rajgangpur in Sundargarh.

The entire coastal belt received above 100 mm precipitation on average during the period.

Very-heavy rain battered Cuttack, Sambalpur, Kandhamal, Jagatsinghpur, Subarnapur and Mayurbhanj districts, the Met office said.

Twenty-one stations received over 115.6 mm of very-heavy rain, while heavy showers of 65-116 mm occurred at 73 places across the state. An intense spell of downpour lashed Bhubaneswar in the morning.

The weatherman has issued a red alert of extremely-heavy rain of over 204 mm till Monday morning for 11 districts Angul, Bolangir, Bargarh, Deogarh, Jharsuguda, Kalahandi, Keonjhar, Nuapada, Sambalpur, Subarnapur and Sundargarh.

An orange alert of very-heavy rain has been sounded for the rest of the 19 districts, including Bhadrak, Balasore, Cuttack, Puri and Khurda, during the period.

The weather office predicted heavy rain in Sundargarh, Jharsuguda, Bargarh and Nuapada on Monday.

It also sent out an alert of local cautionary signal number three (squally weather due to depression) in all the ports of Odisha.

Fisherfolk have been advised not to venture off the coast of Odisha, West Bengal and northern Andhra Pradesh till Monday as the sea can be very rough, with a wind speed of 45-65 kmph expected over the northern and west-central Bay of Bengal.