Updated 3 - Adds focus of investigation,  Simon Busuttil's best wishes

A police investigation has been launched after Prime Minister Joseph Muscat and up to 40 other people were admitted to Mater Dei Hospital last night suffering acute pain in both his eyes.

Dr Muscat's condition improved and he was discharged after four hours of observation. 

Doctors have ordered him to rest for a few days.

All the patients were present at a political activity with the prime minister under a tent in Zurrieq square yesterday morning.

Hospital sources said people started complaining of pain yesterday evening. The prime minister was admitted at about 2am.

Among those who suffered what was described as a burning sensation in their cornea were Tourism Minister Edward Zammit Lewis, Parliamentary Secretaries Chris Fearne and Michael Falzon and MP Joe Sammut.

Most of the patients had been sitting behind Dr Muscat. Some suffered temporary blindness.

The police are understood to be looking into various scenarios, with the most likely cause related to lighting and excessive UV exposure caused by a possible problem with UV filters.

CANDIDATE'S ACCOUNT

MEP candidate Cyrus Engerer was among those affected. He said he had attended the Zurrieq activity and sat behind the prime minister. After Zurrieq he went to Festa Frawli in Mgarr.

On returning, friends remarked that he and his colleagues appeared sunburnt, something which they put down to their visit to Mgarr. At about 6 p.m. he felt his eyes extremely tired and went to bed.

But three hours later he awoke with pain in both eyes.

"I could not even open my eyes and tears were flowing like tap water," he said.

He was given some advice by a doctor but eventually this morning he was told to go to hospital. He was still there at 8.30 a.m. although his condition had improved. He said some people were still going to hospital.

Mr Engerer said he had been told that the cause was suspected to be linked to UV exposure, and people who had worn glasses with UV protection appeared not to have been affected.

A magisterial inquiry is under way.

BUSUTTIL'S BEST WISHES

Opposition leader Simon Busuttil in a tweet expressed his best wishes.

"Best wishes for a speedy recovery to Joseph Muscat, Labour MPs and activists who fell ill after Labour's political activity in Zurrieq," he said.

Speaker Anglu Farrugia, the PL and the PN issued statements expressing best wishes to all affected persons.

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