President Recep Tayyip Erdogan travels to the heart of Turkey's earthquake disaster zone on Friday to formally kick off the toughest election campaign of his two-decade rule.

One poll released on the first official day of campaigning showed the 69-year-old trailing his secular rival by nearly 10 percentage points in the May 14 presidential and parliamentary vote.

The gap appears to have widen due to seething anger at the government's response to a massive earthquake in February that claimed more than 50,000 lives and displaced millions.

But secular opposition leader Kemal Kilicdaroglu -- a 74-year-old former civil servant who has never won a national race -- is facing his own problems from an unlikely source.

Kilicdaroglu has cobbled together a six-party alliance that groups politicians with radically different views and the shared goal of defeating Erdogan.

The opposition views this as their best chance yet to defeat Erdogan and end his Islamic-rooted party's control of growing facets of the highly polarised country's social life.

Turkey's worst economic crisis of Erdogan's era should also boost his rival's hand.

But a last-minute entry of maverick opposition leader Muharrem Ince threatens to upset Kilicdaroglu's plans.

Ince challenged Erdogan in the last election and refused Kilicdaroglu's offer to bow out of the race this week.

Healing wounds

Polls show Ince's support small but growing. The opposition fears the 58-year-old will split the anti-Erdogan vote.

Analysts also point to Erdogan's stellar election record, as well as the government's control of the media and state institutions during the campaign.

Political risk consultancy Eurasia Group said Erdogan's re-election "remains the baseline (scenario), though the odds are falling".

Erdogan's decision to launch his campaign in the ethnically mixed southeastern city of Gaziantep is telling.

He enjoyed some local support during his early efforts to negotiate an end to a Kurdish struggle for an independent state that has claimed tens of thousands of lives.

A breakdown of those talks led to a resurgence of violence and a crackdown on Kurdish leaders that has seen hundreds jailed.

The main pro-Kurdish party -- seen as a kingmaker with roughly 10 percent of the vote -- has given its tacit support to Kilicdaroglu.

But Erdogan appears to be trying to break through to Kurdish voters via pledges of more social support.

He will be attending the groundbreaking ceremony for a relief centre in quake-hit Gaziantep -- one of several he has opened in the past few weeks.

Kitchen chats

Many point to the similarities with an earlier government failing in its response to an earthquake in 1999 in which more than 17,000 people died.

"We are working day and night to heal the wounds caused by the quake," Erdogan said at a similar groundbreaking ceremony in nearby Adiyaman this week.

Kilicdaroglu has taken a radically different approach.

He has played up his humble upbringing in video chats that he records from his formica-tiled kitchen. These regularly gather millions of YouTube and Twitter views.

He appeals directly to the estimated six million teens who grew up during Erdogan's time in power and will be voting for the first time.

Other messages are addressed to religious conservatives who form the core of Erdogan's support.

"I want to appeal to conservative young women," Kilicdaroglu said in one message.

Erdogan prides himself on removing religious restrictions in the officially secular state.

Kilicdaroglu has fought hard to show that his secular party will not curb conservative women's right to stay veiled at work or school.

"We will not allow your achievements and freedoms to be destroyed," Kilicdaroglu told conservative women in the message.

Outsiders

Election officials announced on Friday that the presidential ballot will have four names on it.

Ince's outside candidacy is joined by that of Sinan Ogan -- a far-right politician who obtained his doctorate degree at a prestigious Moscow university.

Ogan's support languishes in the low single digits.

But that of Ince is edging up thanks to support from Turkey's younger male voters, who sympathise with his secular nationalist views.

One poll showed Ince picking up 10 percent of the vote in May.

The opposition Halk TV news site pointed out that Ince was the first politician to reach the quake's epicentre and the most visible in the disaster zone in the past few weeks.

"His voters are not satisfied with the opposition and are against the government," one Halk TV analyst wrote.