Neither are visas required for citizens of Australia, Canada, Israel, Japan, the United States or New Zealand. You can find further information on the most up-to-date list under http://konzuliszolgalat.kormany.hu/en.
Some border crossing points are only open at certain times of the day (local border). You can enter from Austria, Slovenia or Slovakia without border control. The border is basically invisible. You can also exit towards these countries without control. You can cross the border at these sections any time and anywhere, unless specified otherwise.
Passports of air passengers arriving from or heading to any of the Schengen countries are not controlled either, only for security reasons.
From Romania, Ukraine, Serbia or Croatia you can only enter or exit Hungary at the dedicated border crossing points during opening hours, in the order of arrival.
You can find further information related to border crossing under www.police.hu.
Border crossing during the pandemic
As part of the protective measures against COVID-19, on 1 September 2020 Hungary closed its borders and red-listed all countries of the world for 30 days or until further notice, which means they are not recommended for traveling. Apart from a few exceptions, no foreign citizen is allowed to enter Hungary through passenger traffic. The police may grant exemption from this restriction and allow entry in exceptional cases.
Citizens of the Czech Republic, Poland or Slovakia, who can present a negative corona virus test of no more than 5 days, may be granted an exemption.
Further information:
http://www.police.hu/en/content/information-on-general-rules-of-border-crossing