Thiruvananthapuram | An orange alert has been issued in six districts of Keralam, with heavy to very heavy rainfall and thunderstorms likely at isolated places on Monday, officials said.

The India Meteorological Department (IMD) issued the orange alert at 7 am in Pathanamthitta, Alappuzha, Kottayam, Idukki, Ernakulam and Thrissur districts, valid for three hours.

An orange alert indicates the possibility of heavy to very heavy rainfall ranging from 115.6 mm to 204.4 mm in 24 hours.

The IMD said thunderstorms accompanied by rainfall and maximum surface wind speeds of up to 40 kmph are very likely at isolated places in these districts.

Light rainfall is also likely at isolated places in Kollam, Palakkad and Kannur districts, the weather agency said.

Meanwhile, Chief Minister V D Satheesan has directed that the state's rain situation be assessed hourly.

In a statement issued by the Chief Minister's Office on Sunday night, it said Disaster Management Commissioner Vigneshwari convened a meeting of the Idukki and Kottayam district collectors to assess the situation.

SMS alerts have been issued in Idukki and Kottayam districts and the collectors have been directed to assess the situation and take necessary measures, including evacuation, the statement said.

The state witnessed heavy rainfall on Sunday evening, leaving four people dead in separate landslip incidents in Idukki and Kottayam districts.

Heavy rain also triggered a flash flood in the Kottapuzha River in Nilambur in Malappuram district, in which six people were swept away.