US President Barack Obama and his Republican challenger Mitt Romney on Wednesday sparred on domestic issues including healthcare, government regulation and the role of government, as they faced off in the first presidential debate.

The two candidates began to touch on regulation and healthcare when they concentrated on the topic of economy during the first half of the debate.

Romney attacked the Dodd-Frank Wall Street Reform and Consumer Protection Act, signed into law by Obama in 2010, saying it has helped create too-big-to-fail Wall Street banks, while crushing small community banks.

Romney also attacked the Affordable Care Act, a major domestic achievement of Obama, saying it raises cost of healthcare and cuts Medicare.

Obama, on the other hand, defended his record, questioning Romney's "repeal and replace" approach. He stressed the Wall Street needs reform and supervision, while families need protection in the healthcare insurance market.

As they moved on to the topic of the role of the government, Obama stressed the federal government has a role to play in opening up opportunity and create ladders of opportunity.

"There is also something we do better together," said Obama.

Romney said the role of the government is to protect the principals of the Constitution and the Declaration of Independence, but not to substitute for people's initiatives, decrying what he called a "trickle down government."

The debate is the first of three debates Obama and Romney are to participate in this year's presidential election, and their running mates are also going to debate with each other.