Police in Papua New Guinea have opened fire on students protesting against Prime Minister Peter O'Neill.

Several students were injured and opposition MPs said four were killed, but this has not been independently confirmed.

The students were marching from their campus in the capital, Port Moresby, towards parliament where O'Neill faces a possible no confidence motion.

They are demanding that he stand down and answer corruption allegations.

He denies wrongdoing and has said he will not leave office.

Footage obtained by the BBC appeared to show a large crowd of students at the campus running away as shots and tear gas were fired.

Medical officials in Port Moresby told Reuters that at least 10 students had been admitted "in a difficult situation".

Images circulating on social media also showed injured students being carried away.

There have been conflicting reports of casualties. Opposition figures told parliament that four people had died, while other reports said one person was dead.

Reuters quoted an unnamed aid agency as saying it had heard reports four students died at a clinic on the campus in the Waigani suburb of Port Moresby.

The main hospital in the capital told local news site EMTV that it had seen no fatalities.

One eyewitness, David Rupa, told the BBC he was on his way to work when he became caught in the protest at about 08:50 local time (23:50 GMT Tuesday).

He said he could see tear gas and people running for cover and heard shots fired.

"I saw policemen hit and kick girls who couldn't run [fast enough] and were bashed up. I cried and was told I will be shot if I was going to take photos or video."

He also said he had seen smoke coming from a dormitory at the university, and that parents were coming down to the campus to make sure their children were not hurt.

Gary Juffa, an MP and vocal critic of the prime minister, said on Twitter he had been told the shooting began with an argument between one student and a police superintendent.

Reports suggest the students had refused to hand over their protest leader to police.

EMTV said the university had suspended classes to deal with the student boycott, but they were supposed to resume this week.

The students were continuing their boycott, however, as opposition parties lodged a no confidence motion against O'Neill.

O'Neill, who has a majority in parliament, has consistently denied wrongdoing and has refused to stand down.