Image caption Marijuana-smokers in Seattle sparked up as the law took effect

Possession of marijuana has become legal in the US state of Washington, a month after voters opted for decriminalisation.

From midnight (08:00 GMT) anyone aged 21 and over was allowed to carry up to 1oz (28.4g) of cannabis, but smoking it in public will remain illegal.

It has been legal for medical use in the state since 1998.

A law legalising gay marriage also came into effect in Washington state on Thursday.

On 6 November Washington, Maine and Maryland became the first US states to back same-sex marriage in a popular vote, and Washington is the first of those to enact the law.

At midnight local time (08:00 GMT), a group of largely middle-aged people gathered amid reggae music in the city of Seattle to countdown to the marijuana legalisation taking effect, before sparking up.

Mixed messages

The celebration at the Space Needle attraction defied a key provision of the law, which forbids users from smoking the drug outside the privacy of their homes.

But there were mixed messages from officials: hours earlier, Seattle's city attorney issued a warning that pot smoking in public would carry a $100 (£62) fine.

"If drinking in public is disallowed, so is smoking marijuana in public," Pete Holmes said.

However, the Seattle Police Department instructed its officers not to write citations for those smoking in public until further notice, instructing them to give a verbal warning instead.

Media playback is unsupported on your device Media caption Could legalising marijuana save the US economy?

The law also legalises possession of up to 16oz of solid cannabis-infused goods - such as brownies or cookies - and up to 72oz of weed in liquid form.

Ultimately, marijuana will be legally sold from state-licensed stores, and taxed at 25%.

However, there will be nowhere to purchase marijuana legally in Washington for at least another year, as the state has yet to set up the licensing system.

The Washington law also sets the standard for being charged with marijuana impairment while driving, similar to the blood-alcohol level.

'Uncharted water'

It remains unclear how federal law enforcement agencies will deal with liberalisation of drug laws in Washington and - eventually - Colorado.

Colorado voters approved their own ballot measure in November. It is similar to the Washington law, but goes further by allowing individuals to grow small amounts for themselves.

The Colorado measure goes into effect on 5 January.

Any decision to crack down on states with liberal drug laws could affect Washington's plans to raise tax revenues from the licensed and controlled marijuana market.

Experts believe the taxation could bring the state hundreds of millions of dollars a year in new revenue, but the justice department has not said whether it will sue to block the regulatory schemes.

Backers of the Washington law insist it does not encourage or require anyone to break federal law.

But marijuana remains illegal under US law. That means federal agents can still arrest people for it, and it is banned from federal properties, including military bases and national parks.

A regional federal prosecutor in the state, Jenny Durkan, said in a statement that "growing, selling or possessing any amount of marijuana remains illegal under federal law", no matter what law comes into effect in Washington state.

The drug remained in the same category as cocaine, heroin and methamphetamine, she said, adding that only Congress could change that designation.