* Death toll in five days of violence now at 50
* Curfew imposed on Port Said, Ismailia and Suez
* President Mursi calls for dialogue
* Sceptical opposition spurns invitation (Recasts adding new death toll, army arrests law)
By Edmund Blair and Shaimaa Fayed
CAIRO, Jan 28 (Reuters) - A man was shot dead on Monday in a fifth day of violence in Egypt that has killed 50 people and prompted the Islamist president to declare a state of emergency in an attempt to end a wave of unrest sweeping the Arab world's biggest nation.
Under emergency powers announced by President Mohamed Mursi for the cities of Port Said, Ismailia and Suez on Sunday, the army will have the right to arrest civilians and to help police restore order.
A cabinet source told Reuters any trials would be before civilian courts, but the step is likely to anger protesters who accuse Mursi of using high-handed security tactics of the kind they fought against to oust president Hosni Mubarak.
Egypt's politics have become deeply polarised since those heady days two years ago, when protesters were making most of the running in the Arab Spring revolutions that sent shockwaves through the region.
Although Islamists have won parliamentary and presidential elections, the disparate opposition has since united against Mursi. Late last year he moved to expand his powers and push a constitution with Islamist leanings through a referendum punctuated by violent street protests.
Mursi's opponents accuse him of hijacking the revolution, listening only to his Islamist allies and breaking a promise to be a president for all Egyptians. They say too many hold-outs from the Mubarak era remain in their posts.
Islamists say their rivals want to overthrow by undemocratic means Egypt's first freely elected leader.
Some opposition groups have called for more protests in Cairo and elsewhere on Monday to mark the second anniversary of one of the bloodiest days in the revolution that erupted on Jan. 25, 2011, and ended Mubarak's iron rule 18 days later.
Hundreds of demonstrators in Port Said, Ismailia and Suez, cities which all lie on the economically vital Suez Canal, turned out against Mursi's decision on Sunday within moments of him speaking. Activists there pledged to defy a curfew that starts at 9 p.m. (1700 GMT).
Instability in Egypt has raised concerns in Western capitals, where officials worry about the direction of a key regional player that has signed a peace deal with Israel.
The political unrest has been exacerbated by street violence linked to death penalties imposed on soccer supporters convicted of involvement in stadium rioting a year ago.
In Cairo on Monday, police fired volleys of teargas at stone-throwing protesters in and around Tahrir Square, cauldron of the anti-Mubarak uprising.
KILLED BY A GUNSHOT
A 46-year-old bystander was killed by a gunshot, a security source at the Interior Ministry said. It was not clear who fired the shot.
"We want to bring down the regime and end the state that is run by the Muslim Brotherhood," said Ibrahim Eissa, a 26-year-old cook, protecting his face from teargas wafting towards him.
Mursi also called for a national dialogue with his rivals for later on Monday, but the early response from members of the main opposition coalition suggested they saw little point.
Propelled to the presidency in a June election by the Muslim Brotherhood, Mursi has lurched through a series of political crises and violent demonstrations, complicating his task of shoring up the economy and preparing for a parliamentary election to cement the new democracy in a few months.
"The protection of the nation is the responsibility of everyone. We will confront any threat to its security with force and firmness within the remit of the law," Mursi said, offering condolences to families of victims in the canal zone cities.
Appealing to his opponents, the president called for a dialogue on Monday at 6 p.m. (1600 GMT), inviting a range of Islamist allies as well as liberal, leftist and other opposition groups and individuals to discuss the crisis.
The main opposition National Salvation Front coalition said it would not attend.
Mursi's call to hold talks was "cosmetic and not substantive", a leading member of the coalition, Mohamed ElBaradei, told a news conference.
The opposition Front has distanced itself from the latest flare-ups but said Mursi should have acted far sooner to impose security measures that would have ended the violence.
"Of course we feel the president is missing the real problem on the ground, which is his own policies," Front spokesman Khaled Dawoud said. "His call to implement emergency law was an expected move, given what is going on, namely thuggery and criminal activity."
But other activists said Mursi's measures to try to impose control on the turbulent streets could backfire.
"Martial law, state of emergency and army arrests of civilians are not a solution to the crisis," Ahmed Maher of the April 6 movement that helped galvanise the 2011 uprising said. "All this will do is further provoke the youth. The solution has to be a political one that addresses the roots of the problem."
Thousands of mourners joined funerals in Port Said for the latest victims in the Mediterranean port city. Seven people were killed there on Sunday when residents joined marches to bury 33 others who had been killed a day earlier, most by gunshot wounds in a city where arms are rife.
Protests erupted there on Saturday after a court sentenced to death several people from the city for their role in deadly soccer violence last year, a verdict residents saw as unfair. The anger swiftly turned against Mursi and his government.
Rights activists said Mursi's declaration was a backward step for Egypt, which was under emergency law for Mubarak's entire 30-year rule. His police used the sweeping arrest provisions to muzzle dissent and round up opponents, including members of the Brotherhood and even Mursi himself.
Heba Morayef of Human Rights Watch in Cairo said the police, still hated by many Egyptians for their heavy-handed tactics under Mubarak, would once again have the right to arrest people "purely because they look suspicious", undermining efforts to create a more efficient and respected police force.
"It is a classic knee-jerk reaction to think the emergency law will help bring security," she said. "It gives so much discretion to the Ministry of Interior that it ends up causing more abuse, which in turn causes more anger." (Additional reporting by Yasmine Saleh in Cairo and Yusri Mohamed in Ismailia; Editing by Will Waterman and Giles Elgood)